adverb / adjective
extempore
ik-STEM-puh-ree/ɪkˈstempəri/
Done or performed without preparation or rehearsal.
The performer acts extempore, inventing an astronaut routine with an unexpected prop.

Etymology
Literally “out of time,” the Latin phrase meant “offhand” or “according to the needs of the moment.” It describes responding as the occasion arises rather than preparing or rehearsing beforehand.
In context
he says that almost extemporaneously, he broke into tears and he composed this poem extempore and started singing it in his own way.
More examples
- His extempore speech includes a few jokes about the occasion.
- The pianist plays extempore while the guests find their seats.
- Without consulting her notes, the professor answers extempore.
Forms
extemporize verb — Speak or perform without advance preparation.
Similar words
- impromptu
- Emphasizes something arranged or done on the spot.
- unrehearsed
- Specifically emphasizes that a performance has not been practiced.
- spontaneous
- Emphasizes a natural impulse rather than deliberate preparation.