Synonyms of the word 
SPONTANEOUSLY → IMPROMPTU
spontaneously
- adv. In a spontaneous manner; naturally; voluntarily.
impromptu
- adj. Improvised; without prior preparation, planning or rehearsal; extemporaneous; unplanned.
- n. (music) a short musical composition for an informal occasion often with the character of improvisation…
- n. any composition, musical or otherwise, that is created on the spot without preparation.
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