im·promp·tu /ɪmˈprɑm(p)(ˌ)tu, (ˌ)tju/
  即席演出,即興曲(a.)即席的(ad.)即席
  Im·promp·tu adv. ∨ a.  Offhand; without previous study; extemporaneous; extempore; as, an impromptu verse.
  Im·promp·tu, n.
  1. Something made or done offhand, at the moment, or without previous study; an extemporaneous composition, address, or remark.
  2. Mus. A piece composed or played at first thought; a composition in the style of an extempore piece.
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  impromptu
       adj : with little or no preparation or forethought; "his ad-lib
             comments showed poor judgment"; "an extemporaneous
             piano recital"; "an extemporary lecture"; "an extempore
             skit"; "an impromptu speech"; "offhand excuses";
             "trying to sound offhanded and reassuring"; "an
             off-the-cuff toast"; "a few unrehearsed comments" [syn:
              ad-lib, extemporaneous, extemporary, extempore,
              offhand, offhanded, off-the-cuff, unrehearsed]
       n 1: an extemporaneous speech or remark; "a witty impromptu must
            not sound premeditated"
       2: a short musical passage that seems to have been made
          spontaneously without advance preparation
       adv : without advance preparation; "he spoke ad lib" [syn: ad lib,
              ad libitum, spontaneously]