1. from Greek litotes, literally "plainness, simplicity," from litos "smooth, plain, small, meager".
2. It is principally via double negatives. For example, rather than saying that something is attractive (or even very attractive), one might merely say it is "not unattractive".
3. Litotes is a form of understatement.
rhetorical figure in which an affirmative is expressed by the negative of its opposite, from Greek litotes, literally "plainness, simplicity," from litos "smooth, plain, small, meager," from PIE root *(s)lei- "slimy, sticky, slippery" (hence "smooth"); see slime (n.).