"not high," late 13c., from lah (late 12c.), "not rising much, being near the base or ground" (of objects or persons); "lying on the ground or in a deep place" (late 13c.), from Old Norse lagr "low," or a similar Scandinavian source (cf. Swedish låg, Danish lav), from Proto-Germanic *lega- "lying flat, low" (cf. Old Frisian lech, Middle Dutch lage, Dutch laag "low," dialectal German läge "flat"), from PIE *legh- "to lie" (see lie (v.2)).
Meaning "humble in rank" is from c.1200; "undignified" is from 1550s; sense of "dejected, dispirited" is attested from 1737; meaning "coarse, vulgar" is from 1759. In reference to sounds, "not loud," also "having a deep pitch," it is attested from c.1300. Of prices, from c.1400. In geographical usage, low refers to the part of a country near the sea-shore (c.1300; e.g. Low Countries "Holland, Belgium, Luxemburg," 1540s). As an adverb c.1200, from the adjective.