10
voluntarily(adverb, willing, happily, willingly, openly)
9
freely(adjective, adverb, impulsive, willing, impromptu)
6
extemporaneously(adverb, impromptu, impulsively, improv, extemporaneously)
5
willingly(adverb, willing, happily, freely, openly)
5
automatically(adverb, improv, extemporaneously)
5
impulsively(adverb, impulsively)
4
by chance
4
casually
3
ad lib(expression, idiom, adverb, impromptu, improv)
3
ad libitum(expression, adjective, idiom, adverb, improv)
3
accidentally
3
by choice(expression, adverb, happily, freely, willingly)
3
impromptu(adverb, improv, extemporaneously)
3
instinctively
3
involuntarily
3
naturally(adverb, unrestrictedly)
3
rashly(adverb, impulsively)
2
hastily(adverb, impulsively)
2
abruptly(adverb, impulsively)
2
ad-lib(adverb, manner, improv, extemporaneously)
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APASmart Define. (2015). spontaneously thesaurus. Retrieved September 22, 2026, from https://smartdefine.org/spontaneously/thesaurus/synonyms
ChicagoSmart Define. 2015. "spontaneously thesaurus" https://smartdefine.org/spontaneously/thesaurus/synonyms (accessed September 22, 2026).
HarvardSmart Define 2015, spontaneously thesaurus, Smart Define, viewed 22 September, 2026, <https://smartdefine.org/spontaneously/thesaurus/synonyms>.
MLASmart Define. "spontaneously thesaurus" 14 April 2015. Web. 22 September 2026. <https://smartdefine.org/spontaneously/thesaurus/synonyms>