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.).
Litotes adds (negative) words and so increases reading time. So how did it evolve from litos "smooth, plain, small, meager", adjectives all of which contradict the troubles of hypernegation?
I thought about the interpretation of hypernegation as
slimy, which would consist with the PIE root. But this guess appears wrong, because PIE is invented and so succeeds Greek.