SPONTANEOUS

adj. 1 unannounced, unpremeditated, unplanned, impromptu, extemporaneous, extempore, unprepared, unrehearsed, offhand, ad lib, spur-of-the-moment, Colloq off the cuff Miss Malkin's spontaneous speech could not have been better had it been written out 2 natural, unforced, unbidden, instinctive, instinctual, unconscious, reflex, automatic, mechanical, immediate, offhand, unguarded, unthinking, unwitting, involuntary, impetuous, impulsive, Slang knee-jerk How could you doubt the sincerity of such an outburst of spontaneous affection? My spontaneous reaction is to beg you not to take up sky-diving