adv. 25B6; adverb
they applauded spontaneously : WITHOUT BEING ASKED, of one's own accord, voluntarily, on impulse, impulsively, on the spur of the moment, extempore, extemporaneously; informal off the cuff.
he reacted spontaneously : WITHOUT THINKING, automatically, mechanically, unthinkingly, involuntarily, instinctively, naturally, by oneself/itself.