1469, from M.Fr. lavasse (n.), from O.Fr. lavache "torrent (of rain), deluge," from laver "to wash," from L. lavare "to wash" (see lave). The verb is first recorded 1542.
I just think this is a cool word. I heard it used today and thought I should post it here.
Probably the most common phrase that uses this word as a verb is "lavish with praise", but it doesn't have to be limited to that usage by any means.
On a side note, in glancing through references for this word, I discovered a synonym to the adjective form: Lucullan
ADJECTIVE: 1. Lavish; luxurious. 2. Of or relating to Lucullus or his luxurious banquets.
ETYMOLOGY: After Lucius Licinius Lucullus.
I suspect that Lucullan would be more commonly used in England...