What is the X in X-mas?
"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.
Old English hlowan "make a noise like a cow," from Proto-Germanic *khlo- (cf. Middle Dutch loeyen, Dutch loeien, Old Low Franconian luon, Old High German hluojen), from imitative PIE root *kele- (2) "to shout" (see claim (v.)).
sound made by cows, 1540s, from low (v.).
"hill," obsolete except in place names, Old English hlaw "hill, mound," especially "barrow," related to hleonian "to lean" (see lean (v.)). Cf. Latin clivus "hill" from the same PIE root.
early 13c., from low (adj.). Of voices or sounds, from c.1300.