"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.
"spend or bestow profusely," 1540s, from lavish (adj.). Related: Lavished; lavisher; lavishing.