|Origin:||spontaneus, from Latin sponte 'of your own free will'|
something that is spontaneous has not been planned or organized, but happens by itself, or because you suddenly feel you want to do it:
The crowd gave a spontaneous cheer.
My spontaneous reaction was to run away.
someone who is spontaneous does things without planning them first - used to show approval
She laughed spontaneously.
—spontaneity noun [uncountable]