litotes(n = noun.communication)meiosis - 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"
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; a form of understatement; as, “ a citizen of no mean city,” that is, of an illustrious city; or, “not bad”, meaning “good”. [1913 Webster]