extemporaneous adj. + Add to list UK //ɛkstˌɛmpɔːɹˈeɪniəs// ex·tem·po·ra·ne·ous SynonymsEtymology Synonyms ad libextemporaryextemporeimpromptuoff the cuffoffhandoffhandedunrehearsedOriginLATex tempore→LA-LATextemporāneus→ENextemporaneous From Late Latin extemporāneus, from Latin ex tempore (“impromptu”).