2
ingenuous(simple, honest, pure, natural, fresh)
2
irrational(adjective, moving, sensitive, touching, exciting)
2
irresistible(adjective, impulsive, willing, unforced, unprompted)
2
jejune(simple, plain, fresh, innocent, sincere)
2
laid-back(adjective, simple, easy, plain, informal)
2
loose(adjective, simple, easy, plain, careless)
2
not taught
2
off the top of one's head
2
ordinary(adjective, simple, reasonable, common, usual)
2
original(simple, plain, fresh, innocent, sincere)
2
precipitate(noun, adjective, thoughtless, impulsive, rash)
2
predetermined
2
random(careless, chance, casual, arbitrary, unplanned)
2
relaxed(adjective, calm, quiet, light, smooth)
2
rushing(adjective, impulsive, rash, unthinking, sudden)
2
spontaneity
2
straightforward(adjective, open, light, simple, easy)
2
swift(adjective, thoughtless, impulsive, rash, unthinking)
2
unasked for(verb, expression, adjective, phrasal verb)
2
unavoidable(adjective, impulsive, willing, unforced, unprompted)
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APASmart Define. (2015). spontaneous thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/spontaneous/thesaurus/synonyms
ChicagoSmart Define. 2015. "spontaneous thesaurus" https://smartdefine.org/spontaneous/thesaurus/synonyms (accessed September 25, 2026).
HarvardSmart Define 2015, spontaneous thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/spontaneous/thesaurus/synonyms>.
MLASmart Define. "spontaneous thesaurus" 3 August 2015. Web. 25 September 2026. <https://smartdefine.org/spontaneous/thesaurus/synonyms>