(1):

(a.) Proceeding from, or acting by, internal impulse, energy, or natural law, without external force; as, spontaneous motion; spontaneous growth.

(2):

(a.) Proceding from natural feeling, temperament, or disposition, or from a native internal proneness, readiness, or tendency, without constraint; as, a spontaneous gift or proportion.

(3):

(a.) Produced without being planted, or without human labor; as, a spontaneous growth of wood.