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.

adverb

freely , willfully , willingly