Maybe I'm not the only one who keeps forgetting this.
Date: Sat Sep 25 00:01:37 EDT 1999
Subject: A.Word.A.Day--litotes
litotes (LI-tuh-teez, LIT-, li-TOH-teez) noun, plural litotes

A figure of speech consisting of an understatement in which an
affirmative is expressed by negating its opposite, as in This is
no small problem.

[Greek litotes, from litos, plain.]