impromptu (adv.)

1660s, from French impromptu (1650s), from Latin in promptu "in readiness," from assimilated form of in- "into, in, on, upon" (from PIE root *en "in") + promptu, ablative of promptus "ready, prepared; set forth, brought forward," from past participle of promere "to bring out," from pro "before, forward, for" (see pro-) + emere "to obtain" (see exempt (adj.)). From 1764 as an adjective; as a noun from 1680s.