/ ɪmˈprɒmptjuː; NAmE -ˈprɑːmptuː/ adjective
done without preparation or planning
SYN improvised :
an impromptu speech
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WORD ORIGIN
mid 17th cent. (as an adverb): from French , from Latin in promptu in readiness, from promptus brought to light, also prepared, ready, past participle of promere to produce, from pro- out, forth + emere take.