extemporary

/ɪkˈstɛmpəˌrɛri/
adjective
  1. Spoken or done without preparation; impromptu.
    • She gave an extemporary performance that impressed the judges.
    • The comedian's extemporary jokes had the audience laughing uncontrollably.
    • His extemporary decision to change the route saved them from the traffic jam.
Antonyms
What does "extemporary" mean? | whatsthatwordmean | whatsthatwordmean