"spending or bestowing profusely," mid-15c., laves, from Old French lavasse,lavache (n.) "a torrent of rain, deluge" (15c.), from laver "to wash," from Latin lavare "to wash" (from PIE root *leue- "to wash"). Related: Lavishly; lavishness.
It forms all or part of: ablution; alluvium; deluge; dilute; elution; lather; latrine; launder; lautitious; lavage; lavation; lavatory; lave; lavish; lotion; lye.
It is the hypothetical source of/evidence for its existence is provided by: Greek louein "to wash, bathe;" Latin lavare "to wash," luere "to wash;" Old Irish loathar "basin," Breton laouer "trough;" Old English leaþor "lather," læg "lye."
early 15c., "lavish, extravagant, liberal to excess," from Latin profusus "spread out, lavish, extravagant," literally "poured forth," past-participle adjective from profundere "pour forth," from pro "forth" (from PIE root *per- (1) "forward") + fundere "to pour" (from nasalized form of PIE root *gheu- "to pour"). Meaning "bountiful, abundant, copious" is from c. 1600. Related: Profusely; profuseness.
1902, in the classical sense, from Greek ōideion "building for musical performance," from Greek ōidē "song, ode" (see ode). The chain of lavish cinema theaters operated under that name by 1930 (the name had been used earlier for cinema theaters in France and Italy).
late 15c., from Old French sumptueux or directly from Latin sumptuosus "costly, very expensive; lavish, wasteful," from sumptus, past participle of sumere "to borrow, buy, spend, eat, drink, consume, employ, take, take up," contraction of *sub-emere, from sub "under" (see sub-) + emere "to take, buy" (from PIE root *em- "to take, distribute"). Related: Sumptuously; sumptuousness.