Why is the ninth month called September?
late 14c., from Old French lies, plural of lie "sediment," probably from Celtic (cf. Old Irish lige "a bed, a lying"), from PIE root *legh- "to lie" (see lie (v.2)).
Old English hleo "shelter, cover, defense, protection," from Proto-Germanic *khlewaz (cf. Old Norse hle, Danish læ, Old Saxon hleo, Dutch lij "lee, shelter"). No known cognates outside Germanic; original sense uncertain and might have been "warm" (cf. German lau "tepid," Old Norse hly "shelter, warmth"), which might link it to PIE *kele- (1) "warm." As an adjective, 1510s, from the noun.
(Heb. shemarim), from a word meaning to keep or preserve. It was applied to "lees" from the custom of allowing wine to stand on the lees that it might thereby be better preserved (Isa. 25:6). "Men settled on their lees" (Zeph. 1:12) are men "hardened or crusted." The image is derived from the crust formed at the bottom of wines long left undisturbed (Jer. 48:11). The effect of wealthy undisturbed ease on the ungodly is hardening. They become stupidly secure (comp. Ps. 55:19; Amos 6:1). To drink the lees (Ps. 75:8) denotes severe suffering.