extemporaneous

extemporaneous /ɛkˌstɛmpəˈreɪnijəs/ adjective
extemporaneous
/ɛkˌstɛmpəˈreɪnijəs/
adjective
Britannica Dictionary definition of EXTEMPORANEOUS
[more extemporaneous; most extemporaneous]
: made up or done without special preparation — usually used to describe public speaking

— extemporaneously

adverb