'Tautology' definitions:

Definition of 'tautology'

From: WordNet
noun
(logic) a statement that is necessarily true; "the statement `he is brave or he is not brave' is a tautology"
noun
Useless repetition; "to say that something is `adequate enough' is a tautology"

Definition of 'Tautology'

From: GCIDE
  • Tautology \Tau*tol"o*gy\, 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]