50 entries under plain topic. ×

39
natural(adjective, calm, open, simple)
24
impulsive(noun, adjective, moving, simple, easy)
16
extemporaneous(noun, adjective, impulsive, willing)
15
impromptu(adjective, adverb, free, impulsive)
14
unprompted(adjective, natural, thoughtless, impulsive)
10
unrehearsed(adjective, free, impulsive, unprepared)
9
informal(adjective, free, simple, relaxed)
9
casual(adjective, calm, free, fake)
6
candid(simple, easy, honest, pure)
6
easy(adjective, simple, relaxed, casual)
6
unaffected(adjective, simple, easy, honest)
5
intimate(adjective, simple, straightforward, casual)
5
unpretentious(simple, easy, honest, natural)
5
untaught(adjective, simple, fresh, innocent)
3
unrestrained(adjective, calm, simple, relaxed)
2
forthright(adjective, calm, quiet, open, light)
2
jejune(simple, fresh, innocent, sincere)
2
laid-back(adjective, simple, easy, informal)
2
loose(adjective, simple, easy, careless)
2
original(simple, fresh, innocent, sincere)
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APASmart Define. (2015). spontaneous thesaurus. Retrieved September 23, 2026, from https://smartdefine.org/spontaneous/thesaurus/synonyms
ChicagoSmart Define. 2015. "spontaneous thesaurus" https://smartdefine.org/spontaneous/thesaurus/synonyms (accessed September 23, 2026).
HarvardSmart Define 2015, spontaneous thesaurus, Smart Define, viewed 23 September, 2026, <https://smartdefine.org/spontaneous/thesaurus/synonyms>.
MLASmart Define. "spontaneous thesaurus" 3 August 2015. Web. 23 September 2026. <https://smartdefine.org/spontaneous/thesaurus/synonyms>