"impromptu" in the noun sense
1. impromptu
an extemporaneous speech or remark
"a witty impromptu must not sound premeditated"
2. impromptu
a short musical passage that seems to have been made spontaneously without advance preparation
"impromptu" in the adjective sense
1. ad-lib, extemporaneous, extemporary, extempore, impromptu, offhand, offhanded, off-the-cuff, unrehearsed
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"
"impromptu" in the adverb sense
1. ad lib, ad libitum, spontaneously, impromptu
without advance preparation
"he spoke ad lib"
Source: WordNet® (An amazing lexical database of English)
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