| uncalled-for(adjective, willing, arrogant, voluntary, unwelcome) | |
| undesigned(accidental, unintended) | |
| unpredictable(noun, thoughtless, impetuous, unwary) | |
| unwanted(adjective, willing, arrogant, voluntary, unwelcome) | |
| unwilled(unconscious, involuntary) | |
| aboveboard(simple, plain, fresh, innocent, sincere) | |
| accelerated(adjective, sudden) | |
| accidental(adjective, careless, chance, casual, erratic) | |
| acute(adjective, sudden) | |
| ad hoc(expression, free, casual, unplanned, unrehearsed) | |
| ad libitum(expression, informal, unplanned, extemporize, off-the-cuff) | |
| aimless | |
| amiable | |
| anticipated(reasonable, ordinary, usual, normal, logical) | |
| ardent(adjective, moving, violent, fierce, impulsive) | |
| at ease(expression, adjective, calm, quiet, light) | |
| at first glance(expression, free, informal, snap, unrehearsed) | |
| audacious(wild, uncontrolled, unrestricted) | |
| autocratic | |
| automated |
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| APA | Smart Define. (2015). spontaneous thesaurus. Retrieved September 25, 2026, from https://smartdefine.org/spontaneous/thesaurus/synonyms |
| Chicago | Smart Define. 2015. "spontaneous thesaurus" https://smartdefine.org/spontaneous/thesaurus/synonyms (accessed September 25, 2026). |
| Harvard | Smart Define 2015, spontaneous thesaurus, Smart Define, viewed 25 September, 2026, <https://smartdefine.org/spontaneous/thesaurus/synonyms>. |
| MLA | Smart Define. "spontaneous thesaurus" 3 August 2015. Web. 25 September 2026. <https://smartdefine.org/spontaneous/thesaurus/synonyms> |