Synonyms and related words :
ad-lib, astonished, caught napping, caught off balance, extemporaneous, extemporized, haphazard, hasty, impromptu, improvised, makeshift, precipitate, rough-and-ready, snap, struck with surprise, surprised, taken aback, taken by surprise, taken unawares, tripped up, unarranged, unbegun, unconcocted, uncontrived, undeliberated, undevised, unhatched, unmade, unmanufactured, unorganized, unplanned, unpremeditated, unprepared, unprimed, unready, unstudied,