A figure of speech composed of an understatement by which an affirmative is expressed by negating its opposing, such as this really is no small problem.
A figure of speech when the speaker emphasizes the magnitude of a statement by denying its reverse; a figure of message in which understatement is employed with negation to convey a positive characteristic; a type of paradox
A diminution or softening of declaration in the interests of avoiding censure or enhancing the impact by comparison aided by the moderation shown in the shape of appearance; a form of understatement.
In rhetoric, a figure in which an affirmative is expressed because of the negative of the contrary. Thus, “a citizen of no mean town” means one “of an illustrious town.”
understatement for rhetorical impact (especially when expressing an affirmative by negating its contrary)