Impromptu

WORD OF THE DAY

impromptu /adjective  / im-PROMP-too 

Definition
1a: made, done, or formed on or as if on the spur of the moment
1b: improvised
2a: composed or uttered without previous preparation
2b: extemporaneous

Examples
When we got word of Caitlin's good news, we threw an impromptu party to celebrate.

"West capped off his curious musical guest gig, where he subbed for Ariana Grande, with a rambling rant after NBC's broadcast ended. The impromptu speech was captured by Chris Rock, who posted it to his Instagram Story."
— Kim Willis, USA Today, 30 Sept. 2018

Did You Know?
If you think that impromptu looks like a relative of the adjective prompt, you're right; both are ultimately derived from the Latin promere, meaning "to bring forth, take out."
Impromptu was borrowed from French, where it meant "extemporaneously," but French speakers picked it up from the Latin phrase in promptu, a promere descendant meaning "in readiness" or "at hand."
Something that is impromptu is generally "prompted" (that English verb is from Latin promptus, of the same meaning) by an occasion that generates a response in the form of, for example, a party or a speech that has not been planned.
There is also another, much rarer descendant of promere in English: the noun promptuary, meaning "a book of ready reference."