extemporaneous (adj.) Look up extemporaneous at Dictionary.com
"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.