[1] : The Collaborative International Dictionary of English v.0.48

radical \rad"ical\ ra^d"i^kal, a. f., fr. l. radicalis
   having roots, fr. radix, -icis, a root. see radix.
   1. of or pertaining to the root; proceeding directly from the
      root.
      1913 webster

   2. hence: of or pertaining to the root or origin; reaching to
      the center, to the foundation, to the ultimate sources, to
      the principles, or the like; original; fundamental;
      thorough-going; unsparing; extreme; as, radical evils;
      radical reform; a radical party.
      1913 webster

            the most determined exertions of that authority,
            against them, only showed their radical
            independence.                         --burke.
      1913 webster

   3. bot.
      a belonging to, or proceeding from, the root of a plant;
          as, radical tubers or hairs.
      b proceeding from a rootlike stem, or one which does not
          rise above the ground; as, the radical leaves of the
          dandelion and the sidesaddle flower.
          1913 webster

   4. philol. relating, or belonging, to the root, or ultimate
      source of derivation; as, a radical verbal form.
      1913 webster

   5. math. of or pertaining to a radix or root; as, a radical
      quantity; a radical sign. see below.
      1913 webster

   radical axis of two circles. geom. see under axis.

   radical pitch, the pitch or tone with which the utterance
      of a syllable begins. --rush.

   radical quantity alg., a quantity to which the radical
      sign is prefixed; specifically, a quantity which is not a
      perfect power of the degree indicated by the radical sign;
      a surd.

   radical sign math., the sign root originally the
      letter r, the initial of radix, root, placed before any
      quantity, denoting that its root is to be extracted; thus,
      roota, or roota + b. to indicate any other than the
      square root, a corresponding figure is placed over the
      sign; thus, cuberoota, indicates the third or cube root
      of a.

   radical stress elocution, force of utterance falling on
      the initial part of a syllable or sound.

   radical vessels anat., minute vessels which originate in
      the substance of the tissues.
      1913 webster

   syn: primitive; original; natural; underived; fundamental;
        entire.

   usage: radical, entire. these words are frequently
          employed as interchangeable in describing some marked
          alteration in the condition of things. there is,
          however, an obvious difference between them. a radical
          cure, reform, etc., is one which goes to the root of
          the thing in question; and it is entire, in the sense
          that, by affecting the root, it affects in an
          appropriate degree the entire body nourished by the
          root; but it may not be entire in the sense of making
          a change complete in its nature, as well as in its
          extent. hence, we speak of a radical change; a radical
          improvement; radical differences of opinion; while an
          entire change, an entire improvement, an entire
          difference of opinion, might indicate more than was
          actually intended. a certain change may be both
          radical and entire, in every sense.
          1913 webster
see also:
radix radical axis of two circles axis radical pitch radical quantity radical sign 
radical stress radical vessels radical entire 

[2] : The Collaborative International Dictionary of English v.0.48

radical \rad"ical\ ra^d"i^kal, n.
   1. philol.
      a a primitive word; a radix, root, or simple, underived,
          uncompounded word; an etymon.
      b a primitive letter; a letter that belongs to the
          radix.
          1913 webster

                the words we at present make use of, and
                understand only by common agreement, assume a
                new air and life in the understanding, when you
                trace them to their radicals, where you find
                every word strongly stamped with nature; full of
                energy, meaning, character, painting, and
                poetry.                           --cleland.
          1913 webster

   2. politics one who advocates radical changes in government
      or social institutions, especially such changes as are
      intended to level class inequalities; -- opposed to
      conservative.
      1913 webster

            in politics they the independents were, to use the
            phrase of their own time, "root-and-branch men," or,
            to use the kindred phrase of our own, radicals.
                                                  --macaulay.
      1913 webster

   3. chem.
      a a characteristic, essential, and fundamental
          constituent of any compound; hence, sometimes, an
          atom.
          1913 webster

                as a general rule, the metallic atoms are basic
                radicals, while the nonmetallic atoms are acid
                radicals.                         --j. p. cooke.
          1913 webster
      b specifically, a group of two or more atoms, not
          completely saturated, which are so linked that their
          union implies certain properties, and are conveniently
          regarded as playing the part of a single atom; a
          residue; -- called also a compound radical. cf.
          residue.
          1913 webster

   4. alg. a radical quantity. see under radical, a.
      1913 webster

            an indicated root of a perfect power of the degree
            indicated is not a radical but a rational quantity
            under a radical form.                 --davies 
                                                  peck math.
                                                  dict.
      1913 webster

   5. anat. a radical vessel. see under radical, a.
      1913 webster
see also:
compound radical residue radical 

[3] : The Collaborative International Dictionary of English v.0.48

residue \res"idue\ r?z"?-d?, n. f. r'esidu, l. residuum,
   fr. residuus that is left behind, remaining, fr. residere to
   remain behind. see reside, and cf. residuum.
   1. that which remains after a part is taken, separated,
      removed, or designated; remnant; remainder.
      1913 webster

            the residue of them will i deliver to the sword.
                                                  --jer. xv. 9.
      1913 webster

            if church power had then prevailed over its victims,
            not a residue of english liberty would have been
            saved.                                --i. taylor.
      1913 webster

   2. law that part of a testeator's estate wwhich is not
      disposed of in his will by particular and special legacies
      and devises, and which remains after payment of debts and
      legacies.
      1913 webster

   3. chem. that which remains of a molecule after the removal
      of a portion of its constituents; hence, an atom or group
      regarded as a portion of a molecule; a moiety or
      group; -- used as nearly equivalent to radical, but in
      a more general sense.
      1913 webster +pjc

   note: the term radical is sometimes restricted to groups
         containing carbon, the term residue and moiety being
         applied to the others.
         1913 webster

   4. theory of numbers any positive or negative number that
      differs from a given number by a multiple of a given
      modulus; thus, if 7 is the modulus, and 9 the given
      number, the numbers -5, 2, 16, 23, etc., are residues.
      1913 webster

   syn: rest; remainder; remnant; balance; residuum; remains;
        leavings; relics.
        1913 webster
see also:
reside residuum moiety group radical 

[4] : WordNet (r) 2.0

radical
     adj 1: used of opinions and actions far beyond the norm;
            "extremist political views"; "radical opinions on
            education"; "an ultra conservative" syn: extremist,
             ultra
     2: markedly new or introducing radical change; "a revolutionary
        discovery"; "radical political views" syn: revolutionary
     3: arising from or going to the root; "a radical flaw in the
        plan"
     4: of or relating to or constituting a linguistic root; "a
        radical verb form"
     5: especially of leaves; located at the base of a plant or
        stem; especially arising directly from the root or
        rootstock or a root-like stem; "basal placentation";
        "radical leaves" syn: basal ant: cauline
     n 1: chemistry two or more atoms bound together as a single
          unit and forming part of a molecule syn: group, chemical
          group
     2: an atom or group of atoms with at least one unpaired
        electron; in the body it is usually an oxygen molecule
        than has lost an electron and will stabilize itself by
        stealing an electron from a nearby molecule; "in the body
        free radicals are high-energy particles that ricochet
        wildly and damage cells" syn: free radical
     3: a person who has radical ideas or opinions
     4: a character conveying the lexical meaning of a logogram
     5: a sign placed in front of an expression to denote that a
        root is to be extracted syn: radical sign
     6: linguistics the form of a word after all affixes are
        removed; "thematic vowels are part of the stem" syn: root,
         root word, base, stem, theme
see also:
extremist ultra revolutionary basal cauline group 
chemical group free radical radical sign root root word 
base stem theme 

[5] : Moby Thesaurus II by Grady Ward, 1.0

429 moby thesaurus words for "radical":
   bolshevik, bolshevist, fabian, gospel side, ic analysis, jacobin,
   kekule formula, wobbly, ab ovo, aboriginal, absolute, accidence,
   acid, acidity, advanced, affix, affixation, agent, agitator,
   algorismic, algorithmic, aliquot, alkali, alkalinity,
   all-embracing, all-encompassing, all-inclusive, all-out,
   all-pervading, alloisomer, allomorph, anarchist, anarchistic,
   anarcho-syndicalist, anion, antacid, arrowhead, at the height,
   at the limit, atom, atomic cluster, basal, base, basement, basic,
   basilar, basis, bearing wall, bed, bedding, bedrock, beginning,
   benzene ring, biochemical, born, bottom, bound morpheme,
   branched chain, broad, broad-based, broad-minded, cantorial side,
   cardinal, cataclysmic, catastrophic, cation, central, chain,
   character, chemical, chemical element, chromoisomer, clean, clear,
   closed chain, commencement, communist, complete, compound,
   compound radical, comprehensive, conception, congenital,
   conjugation, constituent, constitutional, constitutive, consummate,
   copolymer, corrective, counterclockwise, crucial, cuneiform,
   cutting, cycle, decimal, declension, deep, deep-dyed, deep-seated,
   demotic character, derivation, determinative, difference of form,
   differential, digital, dimer, downright, drastic, dyad,
   dyed-in-the-wool, egregious, element, elemental, elementary,
   embryonic, emendatory, enclitic, entire, essential, even,
   exhaustive, exponential, extreme, extreme left-winger, extremist,
   extremistic, fanatic, fanatical, far out, figural, figurate,
   figurative, finite, floor, flooring, fond, footing, formative,
   foundation, foundational, fractional, free form, fundament,
   fundamental, furthest, generative, genesis, genetic, germinal,
   gradualistic, grammalogue, grass roots, greatest, ground, grounds,
   groundwork, gut, hardpan, head, heavy chemicals, heptad,
   heterocycle, hexad, hieratic symbol, hieroglyph, hieroglyphic,
   hieroglyphics, high polymer, hiragana, homocycle, homopolymer,
   hydracid, ideogram, ideograph, imaginary,
   immediate constituent analysis, immoderate, impair, impossible,
   in embryo, in ovo, inception, infinite, infix, infixation,
   inflection, inherent, inorganic chemical, insurgent,
   insurrectionary, insurrectionist, integral, intensive, intrinsic,
   ion, irrational, isomer, kana, katakana, larboard, lattice, left,
   left hand, left wing, left-hand, left-hand side, left-wing,
   left-wing extremist, left-winger, left-wingish, leftist,
   levorotatory, liberal, logarithmic, logogram, logograph,
   logometric, lunatic fringe, macromolecule, material, meliorist,
   melioristic, metamer, mild radical, mildly radical, militant,
   molecule, monad, monomer, morph, morpheme, morphemic analysis,
   morphemics, morphology, morphophonemics, most, natural, near,
   near side, negative, neutralizer, nigh, nihilist, nihilistic,
   nonacid, numeral, numerary, numerative, numeric, octad, odd,
   of the essence, ogham, omnibus, omnipresent, ordinal, organic,
   organic chemical, origin, original, origination, out-and-out,
   outright, oxyacid, pair, paradigm, parlor bolshevik, parlor pink,
   pavement, pentad, perfect, pervasive, phonetic, phonetic symbol,
   pictogram, pictograph, pink, pinko, plain, plumb, polymer, port,
   port tack, portside, positive, possible, prefix, prefixation,
   pregnant, primal, primary, prime, primeval, primitive, primordial,
   principal, principle, pristine, proclitic, profound,
   progressionist, progressist, progressive, progressivist,
   protogenic, provenience, pseudoisomer, pure, rabid, radix,
   rational, reagent, rebel, reciprocal, red, reformational,
   reformative, reformatory, reformer, reformist, reformistic,
   regular, revisional, revisionist, revisory, revolutional,
   revolutionary, revolutionist, revulsionary, revulsive, ring,
   riprap, rise, rock bottom, root, rudiment, rudimentary, rune,
   sans-culotte, seat, secessionist, seminal, separatist, severe,
   sheer, shorthand, side chain, sill, simple radical, sinister,
   sinistral, sinistrocerebral, sinistrocular, sinistrogyrate,
   sinistrorse, solid ground, solid rock, source, space-lattice, stem,
   stereobate, stock, straight, straight chain, stylobate,
   submultiple, substantial, substantive, substratum, substruction,
   substructure, subversive, suffix, suffixation, sulfacid, surd,
   sweeping, syndicalist, taproot, terra firma, tetrad, theme,
   thorough, thoroughgoing, through-and-through, tolerant, too much,
   total, transcendental, transilient, triad, trimer, ubiquitous,
   ultra, ultra-ultra, ultraconservative, ultraist, ultraistic,
   unconditional, underbuilding, undercarriage, undergirding,
   underlying, underpinning, understruction, understructure,
   universal, unmitigated, unqualified, unreserved, unrestricted,
   utmost, utopian, utopist, utter, uttermost, veritable, verso,
   vital, way out, wedge, wholesale, wide, word letter,
   word-formation, wrong side, yippie, zealot

Radical >> R Words
Radical, definition of term: Radical
radical_pag1.html

Free Radical >> F Words
Free Radical, definition of term: Free Radical
free+radical_pag1.html