For a reaction, synonyms could include automatic, reflexive, or instinctive.
For a spontaneous person : impulsive, impetuous, or extemporaneous.
Spontaneous
wish, passion, motivation, inspiration, influence, feeling, desire, appeal
We're part of such a spontaneous generation!
Spontaneous is an adjective--a spontaneousperson.
She was very spontaneous in her life, going wherever her whims might take her. The spontaneous reaction of sodium and water can be very dangerous.
Spontaneous
spontaneous
wish, passion, motivation, inspiration, influence, feeling, desire, appeal
mechanical, automated, push-button, self-propelling, involuntary, natural, unconscious, spontaneous, reflex, instinctive, unwilled
spontaneous
Spontaneous
spontaneous ACCOUNT
'Spontaneous' means "arising from a momentary impulse". There is no animal which represents 'spontaneous'.
spontaneous
A tween can be spontaneous by being themselves.
Spontneous
Spontaneous Inventions was created in 1986.