/ ekˌstem.pəˈreɪ.ni.əs / adjective formal
done or said without any preparation or thought:
an extemporaneous speech 即兴演讲
extempore

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/ ekˈstem.p ə r.i / adjective formal
done or said without any preparation or thought:
an extempore performance 即兴表演
impromptu

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/ ɪmˈprɑːmp.tuː / adjective
done or said without earlier planning or preparation:
an impromptu party/performance 临时晚会/即兴表演
improvisatory

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/ ˌɪm.prəˈvaɪ.zə.tɔːr.i / adjective
(of speech or music) done or performed without having been planned exactly, making something up as it is being performed:
an improvisatory dance/song 即兴舞蹈/歌曲

( 即兴的 Cambridge Chinese (Simplified)-English Dictionary 的翻译 © Cambridge University Press)