Spontaneous1. (a.) Impulsive; extemporaneous; proceeding from natural feeling, temperament, or disposition, or from a native internal proneness, readiness, or tendency, without constraint; as, a spontaneous gift or proportion.
2. (a.) Proceeding from, or acting by, internal impulse, energy, or natural law, without external force; as, spontaneous motion; spontaneous growth.
3. (a.) Produced without being planted, or without human labor; as, a spontaneous growth of wood.
Thesaurus Entries
ad lib, arbitrary, automated, automatic, automatous, autonomous, bat, baton, billy, billy club, bludgeon, casual, club, cybernated, discretional, discretionary, elective, extemporaneous, extempore, free, free will, gratuitous, gut, ill-advised, ill-considered, ill-devised, immediate, impetuous, impromptu, improvised, impulsive, inadvertent, indeliberate, independent, inherent, innate, instinctive, instinctual, involuntary, libidinal, mace, mechanical, natural, nightstick, nonmandatory, off the cuff, offered, offhand, optional, proffered, reflex, reflexive, self-acting, self-active, self-adjusting, self-closing, self-controlled, self-cooking, self-determined, self-determining, self-directed, self-directing, self-dumping, self-governed, self-governing, self-lighting, self-operative, self-regulative, self-starting, self-winding, self-working, semiautomatic, simple, snap, spontoon, spur-of-the-moment, subliminal, truncheon, unadvised, unannounced, unasked, unbesought, unbidden, uncalculated, uncalled-for, uncoerced, uncompelled, unconscious, unconsidered, unconstrained, undeliberate, undeliberated, undesigned, unforced, unguarded, uninfluenced, unintended, unintentional, uninvited, unlearned, unmeditated, unplanned, unpremeditated, unprepared, unpressured, unprompted, unrehearsed, unrequested, unrequired, unsolicited, unsophisticated, unsought, unstudied, unthinking, unwilled, unwitting, voluntary, volunteer, willful