Source : Webster's Revised Unabridged Dictionary (1913)

Litotes \Li"to*tes\, n. [NL., fr. Gr. ?, from ? plain, simple.]
   (Rhet.)
   A diminution or softening of statement for the sake of
   avoiding censure or increasing the effect by contrast with
   the moderation shown in the form of expression; as, `` a
   citizen of no mean city,'' that is, of an illustrious city.

Source : WordNet®

litotes
     n : understatement for rhetorical effect (especially when
         expressing an affirmative by negating its contrary);
         "saying `I was not a little upset' when you mean `I was
         very upset' is an example of litotes" [syn: {meiosis}]