The definition of impromptu is something done without advance thought or without a plan.(adjective)
When everyone gets together and decides to throw a party at the spur of the moment, this is an example of animpromptu party.
See impromptu in Webster's New World College Dictionary
Origin: Fr < L in promptu, in readiness < in, in + promptu, abl. of promptus, readiness < promptus, brought out, ready, prompt
See impromptu in American Heritage Dictionary 4
Origin: , from Latin in prōmptū, at hand
Origin: : in, in; see in-2
Origin: + prōmptū
Origin: , ablative of prōmptus, readiness
Origin: , from
Origin: past participle of prōmere, to bring forth; see prompt.
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