Least
Old English lǣst, lǣsest, of Germanic origin; related to less.
wiktionary
From Middle English leste, lest, last, from Old English lǣst, a contraction of læsast, læsest, lærest(“least”), from Proto-Germanic *laisistaz(“smallest; least”), related to Old English læs(“less”). Cognate with Old Frisian leist, Old Saxon lēs. More at less.
Contraction of at least.
etymonline
least (adj.)
Old English læst, earlier læsest "smallest, lowest in power or position" (superlative of little (adj.)), from Proto-Germanic superlative *laisista-, from PIE root *leis- (2) "small" (see less). Qualifying phrase at least "not to say more than is certainly true" is Middle English æt læstan, from the notion of "at the lowest degree." As a noun, "smallest admissible quantity or degree," from early 12c.; as an adverb, Old English læst "in the least degree."
