coming or resulting from a natural impulse or tendency; without effort or premeditation; natural and unconstrained; unplanned

a spontaneous burst of applause.

(of a person) given to acting upon sudden impulses.

(of natural phenomena) arising from internal forces or causes; independent of external agencies; self-acting.

growing naturally or without cultivation, as plants and fruits; indigenous.

produced by natural process.

adjective

deliberate , intended , planned , premeditated

adjective

ad-lib * , automatic , break loose , casual , down , extemporaneous , extempore , free , free spirited , from the hip , impetuous , impromptu , improvised , inevitable , instinctive , involuntary , irresistible , natural , offhand , off-the-cuff , off top of head , simple , unartful , unavoidable , unbidden , uncompelled , unconscious , unconstrained , uncontrived , uncontrolled , unforced , unintentional , unplanned , unpremediated , unprompted , unsophisticated , unstudied , up front , voluntary , impulsive , reflex , unpremeditated , volitional , willful , easy , informal , relaxed , unceremonious , unrestrained , careless , gratuitous , idiopathic , indigenous , intuitive , knee-jerk , makeshift , native , spur-of-the-moment , stopgap , unforce , unprepared , unrehearsed , unthinking