adj. 25B6; adjective
a spontaneous display of affection : UNPLANNED, unpremeditated, unrehearsed, impulsive, impetuous, unstudied, impromptu, spur-of-the-moment, extempore, extemporaneous; unforced, voluntary, unconstrained, unprompted, unbidden, unsolicited; informal off-the-cuff.
a spontaneous reaction to danger : REFLEX, automatic, mechanical, natural, knee-jerk, involuntary, unthinking, unconscious, instinctive, instinctual; informal gut.
a spontaneous kind of person : NATURAL, uninhibited, relaxed, unselfconscious, unaffected, open, genuine, easy, free and easy; impulsive, impetuous.
planned, calculated, conscious, voluntary, inhibited.