least adj.

Old English lytel "not large, not much, small in size or number; short in distance or time; unimportant,"

from Proto-Germanic *lutilla- (source also of Old Saxon luttil, Dutch luttel, Old High German luzzil, German lützel "little"), perhaps originally a diminutive of the root of Old English lyt "little, few," from PIE *leud- "small."

"Often synonymous with small, but capable of emotional implications which small is not" [OED]. Now with less, least, but formerly and in dialect littler, littlest. In terms of endearment from 1560s. Meaning "younger" (of a brother, sister, etc.) is from 1610s. As an adverb, Old English lytel.

Little while "a short time" is from 12c. Phrase the little woman "wife" attested from 1795. Little people "the faeries" is from 1726; as "children" it is attested from 1752; as "ordinary people" (opposed to the great) from 1827. Little death "orgasm" (1932) translates French petite mort. Little Neck clams (1884) are so called for Little Neck, a "neck" of land on Long Island's North Shore, where they first came into favor. Little green men "space aliens" is from 1950. Little boys' room (or girls') as a euphemism for "lavatory" is from 1957. Little breeches for "boy" is by 1785. Little black dress is from 1939.

At the beginning of summer, smart women who stay in town like to wear sheer "little black dresses." Because most "little black dresses" look alike, retailers struggle each year to find something which will make them seem new. [Life magazine, June 13, 1939]

Old English læs (adv.) "less, lest;" læssa (adj.) "less, smaller, fewer" (Northumbrian leassa), from Proto-Germanic *laisizan (source also of Old Saxon, Old Frisian les "less;" Middle Dutch lise "soft, gentle," German leise "soft"), from PIE root *leis- (2) "small" (source also of Lithuanian liesas "thin") + comparative suffix.

From the first, the adverb has been used often with negatives (none the less). Much less "still more undesirable" is from 1630s. Formerly also "younger," as a translation of Latin minor, a sense now obsolete except in James the Less. Used as a comparative of little, but not related to it. The noun is Old English læsse.

1825, obsolete colloquial, from least + way (n.). Regarded as vulgar, but simply a one-word form of Chaucer's leest weye (late 14c.). Compare leastwise (adv.) "in the least, at least," attested from 1610s, 1530s as two words.