Impromptu1. (adv.) Offhand; without previous study; extemporaneous; extempore; as, an impromptu speech.
2. (n.) Something made or done offhand, at the moment, or without previous study; an extemporaneous composition, address, or remark.
3. (n.) A piece composed or played at first thought; a composition in the style of an extempore piece.
Thesaurus Entries
ad lib, ad libitum, ad-lib, ad-libbing, arrangement, at short notice, at sight, by ear, cadenza, caught napping, caught off balance, caught short, extemporaneous, extemporaneously, extemporaneousness, extemporarily, extemporariness, extemporary, extempore, extemporization, extemporized, flourish, haphazard, hasty, hot lick, improvisation, improvisatorial, improvise, improvised, improvision, improviso, interpolation, jury-rig, jury-rigged, lick, makeshift, measure, off the cuff, off the hip, off-the-cuff, offhand, on sight, out of hand, playing by ear, precipitate, pro tempore, quick, riff, rough-and-ready, snap, stopgap, surprised, taken aback, taken by surprise, taken unawares, temporary arrangement, temporary measure, tripped up, unarranged, unbegun, unconcocted, uncontrived, undeliberated, undevised, unhatched, unmade, unmanufactured, unorganized, unplanned, unpremeditated, unprepared, unprimed, unready, unrehearsed, unstudied, vamp