ad-lib
1
vb busk, extemporize, improvise, make up, speak extemporaneously, speak impromptu, speak off the cuff, vamp, wing it (informal)
2
adj extemporaneous, extempore, extemporized, impromptu, improvised, made up, off-the-cuff (informal) off the top of one's head, unprepared, unrehearsed
3
adv extemporaneously, extempore, impromptu, off the cuff, off the top of one's head (informal) without preparation, without rehearsal