extemporaneous

/ɪkˌstɛmpəˈreɪniəs/
adjective
  1. Spoken or done without preparation or planning; impromptu.
    • Her extemporaneous remarks at the meeting surprised everyone with their clarity.
    • The teacher gave an extemporaneous speech when the guest speaker didn't show up.
    • He is known for his ability to deliver extemporaneous comedy routines that feel perfectly timed.
Antonyms
What does "extemporaneous" mean? | whatsthatwordmean | whatsthatwordmean