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