extemporaneous (adj.)youdaoicibaDictYouDict[extemporaneous 词源字典]
"made, done, procured, or furnished 'at the time,'" hence "unpremeditated," 1650s, from Medieval Latin extemporaneus, from Latin ex tempore (see extempore). Earlier was extemporal (1560s); extemporanean (1620s). Related: Extemporaneously; extemporaneousness.[extemporaneous etymology, extemporaneous origin, 英语词源]