spontaneous (adj.)

• arbitrary
• automated
• automatic
• autonomous
• casual
• discretional
• discretionary
• elective
• extemporaneous
• extempore
• free
• gratuitous
• ill-advised
• ill-considered
• immediate
• impetuous
• impromptu
• improvised
• impulsive
• inadvertent
• independent
• inherent
• innate
• instinctive
• involuntary
• libidinal
• mechanical
• natural
• nonmandatory
• offhand
• optional
• reflex
• reflexive
• self-acting
• self-directed
• self-governing
• self-winding
• semiautomatic
• simple
• spur-of-the-moment
• subliminal
• unadvised
• unannounced
• unasked
• uncalled-for
• uncoerced
• unconscious
• unconsidered
• unconstrained
• undesigned
• unforced
• unguarded
• uninfluenced
• unintended
• unintentional
• uninvited
• unlearned
• unplanned
• unpremeditated
• unprepared
• unprompted
• unrehearsed
• unrequested
• unsolicited
• unsophisticated
• unsought
• unstudied
• unthinking
• unwilled
• unwitting
• voluntary
• volunteer
• willful