What is another word for "spontaneous"?

Roget's Thesaurus (1911) lists these synonyms for "spontaneous": accord, autocratic, bid, casual, choice, comes, creature, deliberately, discretion, discretional, discretionary, est, extemporaneous, extempore, extemporize, flash, free, good, head, impromptu, improvisate, improvisation, improvisatore, improvisatory, improvise, improviso, impulse, impulsive, indeliberate, inspiration, instinctive, intended, intentionally, man, mind, minded, moment, muss, natural, occasion.