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

informal \inform"al\, a. pref. in- not + formal.
   1. not in the regular, usual, or established form; not
      according to official, conventional, prescribed, or
      customary forms or rules; irregular; hence, without
      ceremony; as, an informal writing, proceeding, or visit.
      1913 webster

   2. deranged in mind; out of one's senses. obs.
      1913 webster

            these poor informal women.            --shak.
      1913 webster

[2] : WordNet (r) 2.0

informal
     adj 1: not formal; "conservative people unaccustomed to informal
            dress"; "an informal free-and-easy manner"; "an
            informal gathering of friends" ant: formal
     2: not officially recognized or controlled; "an informal
        agreement"; "a loose organization of the local farmers"
        syn: loose
     3: used of spoken and written language ant: formal
     4: having or fostering a warm or friendly atmosphere;
        especially through smallness and informality; "had a cozy
        chat"; "a relaxed informal manner"; "an intimate cocktail
        lounge"; "the small room was cozy and intimate" syn: cozy,
         intimate
see also:
formal loose cozy intimate 

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

108 moby thesaurus words for "informal":
   bohemian, affable, beat, beat-up, bedraggled, blowzy, breakaway,
   careless, casual, chintzy, colloquial, common, conversational,
   cordial, degage, dilapidated, drabbletailed, draggled,
   draggletailed, easy, easygoing, en deshabille, everyday, familiar,
   far out, folksy, free, free and easy, fringy, frowzy, frumpish,
   frumpy, garden-variety, gracious, grubby, haymish, heretical,
   heterodox, hippie, homely, homey, in dishabille, in rags,
   irregular, kinky, loose, lumpen, maverick, messy, mussy, natural,
   negligent, nonstandard, not cricket, not done, not kosher, offbeat,
   offhand, offhanded, ordinary, original, plain, poky, private,
   ragged, raggedy, relaxed, ruinous, scraggly, seedy, shabby, shoddy,
   simple, slack, slatternly, slipshod, sloppy, slovenly, sluttish,
   sociable, sordid, special, spoken, spontaneous, sporty, squalid,
   substandard, tacky, tattered, unaffected, unassuming, unauthorized,
   unceremonious, unconstrained, unconventional, uneducated,
   unfashionable, unkempt, unliterary, unneat, unofficial, unorthodox,
   unpretentious, unsightly, unstudied, untidy, vernacular, way out

Informal >> I Words
Informal, definition of term: Informal
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