Synonyms and related words :
ad lib, ad libitum, ad-lib, casual, caught napping, caught off balance, caught short, extemporary, extempore, extemporized, haphazard, hasty, impromptu, improvisatorial, improvise, improvised, improviso, impulsive, informal, jury-rigged, makeshift, off the cuff, off-the-cuff, offhand, precipitate, rough-and-ready, snap, spontaneous, spur-of-the-moment, stopgap, 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, unrehearsed, unstudied