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

tautology \tautol"ogy\, n. l. tautologia, gr. ?: cf. f.
   tautologie. rhet.
   a repetition of the same meaning in different words; needless
   repetition of an idea in different words or phrases; a
   representation of anything as the cause, condition, or
   consequence of itself, as in the following lines: 

         the dawn is overcast, the morning lowers,
         and heavily in clouds brings on the day. --addison.
   1913 webster

   syn: repetition.

   usage: tautology, repetition. there may be frequent
          repetitions as in legal instruments which are
          warranted either by necessity or convenience; but
          tautology is always a fault, being a sameness of
          expression which adds nothing to the sense or the
          sound.
          1913 webster
see also:
tautology repetition 

[2] : WordNet (r) 2.0

tautology
     n 1: logic a statement that is necessarily true; "the statement
          `he is brave or he is not brave' is a tautology"
     2: useless repetition; "to say that something is `adequate
        enough' is a tautology"

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

83 moby thesaurus words for "tautology":
   abundance, amplitude, battology, bedizenment, circumambages,
   circumbendibus, circumlocution, cloud of words, copiousness,
   diffuseness, diffusion, diffusiveness, duplication,
   duplication of effort, effusion, effusiveness, embellishment,
   expletive, extravagance, exuberance, fat, featherbedding,
   fecundity, fertility, filling, fluency, formlessness, frill,
   frills, frippery, gingerbread, gush, gushing, iteration, logorrhea,
   long-windedness, luxury, macrology, needlessness, ornamentation,
   outpour, overadornment, overflow, overlap, padding, palilogy,
   payroll padding, periphrase, periphrasis, pleonasm, prodigality,
   productivity, profuseness, profusion, prolificacy, prolificity,
   prolixity, rampancy, rankness, redundance, redundancy, reiteration,
   reiterativeness, repetition, repetition for effect,
   repetitiousness, repetitiveness, roundabout, stammering,
   stuttering, superabundance, superfluity, superfluousness,
   superflux, talkativeness, tautologism, teemingness, tirade,
   unnecessariness, verbality, verbiage, verbosity, wordiness

[4] : The Free On-line Dictionary of Computing (27 SEP 03)

tautology
     
         a proposition which is always true.
     
        compare: paradox.
     
        the linguistic smarandache tautologies,
        http://www.gallup.unm.edu/~smarandache/tautolog.txt.
     
        1999-07-28
     
     
see also:
proposition paradox lt;the linguistic smarandache tautologies,gt; 

Tautology >> T Words
Tautology, definition of term: Tautology
tautology_pag1.html