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.
The Dutch word is said to be cognate with Old English lutian "lurk," and related to Old English loddere "beggar;" Old High German lotar "empty, vain," luzen "lurk;" German Lotterbube "vagabond, rascal," lauschen "eavesdrop;" Gothic luton "mislead;" Old English lyðre "base, bad, wicked." Related: Loitered; loitering.
1781, "to make small, reduce in proportion," from be- + little (v.); first recorded in writings of Thomas Jefferson (and probably coined by him), Jefferson used it in "Notes on the State of Virginia" to characterize the view promoted as scientific by French naturalist Georges-Louis Leclerc Buffon that American species (including humans) were naturally smaller than and inferior to European ones, which Jefferson was at pains to refute. ("So far the Count de Buffon has carried this new theory of the tendency of nature to belittle her productions on this side of the Atlantic.") The word was roundly execrated in England, as be- is properly to be used only with verbs:
Belittle! What an expression! It may be an elegant one in Virginia, and even perfectly intelligible; but for our part, all we can do is to guess at its meaning. For shame, Mr. Jefferson! [European Magazine and London Review, August 1787; to guess was considered another Yankee barbarism]
Jefferson also sent Buffon a stuffed moose. The figurative sense of "depreciate, scorn as worthless" (as the reviewers did to this word) is from 1797 and is now almost the only sense. Related: Belittled; belittling.
Jefferson, as if disposed to assail the sovereignty of the English tongue as well as the sovereignty of the English sword, never hesitated to coin a word when it suited his purposes so to do; and though many of his brood are questionable on the ground of analogy and as intermixing languages; yet they were expressive, and became familiar. [Hugh Blair Grigsby, "The Virginia Convention of 1776," 1855]
in musical directions, "a little, slightly," 1724, from Italian poco, from Latin paucus "few, little" (source also of French peu), from PIE *pau-ko-, suffixed form of root *pau- (1) "few, little."
"the little finger," 1808, in Scottish, from Dutch pinkje, diminutive of pink "little finger," a word of uncertain origin.