Definitions

spontaneous

[spon-tey-nee-uhs] / spɒnˈteɪ ni əs /

ADJECTIVE

impulsive, willing

Synonyms

STRONGEST

casual impromptu instinctive offhand simple unplanned voluntary

WEAK

ad-lib automatic break loose down extemporaneous extempore free free-spirited from the hip impetuous improvised inevitable involuntary irresistible natural off top of head off-the-cuff unartful unavoidable unbidden uncompelled unconscious unconstrained uncontrived uncontrolled unforced unintentional unpremediated unprompted unsophisticated unstudied up front

Antonyms

STRONGEST

deliberate planned

WEAK

intended premeditated

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

"Gravitational waves modulate the quantum field, which in turn affects spontaneous emission," said Jerzy Paczos, a PhD student at Stockholm University.

From Science Daily • Apr. 10, 2026

This one-sided empathy is not a spontaneous response to compelling facts, however.

From Slate • Apr. 3, 2026

Vance, though, is clearly incapable of such a spontaneous response.

From Salon • Apr. 1, 2026

That kind of flexibility leads to spontaneous nights where what started off as an intimate hang expands into an all-out party.

From Los Angeles Times • Mar. 26, 2026

And by freezing cells at various points, they believed they could see the actual moment when a normal cell growing in culture became malignant, a phenomenon they called spontaneous transformation.

From "The Immortal Life of Henrietta Lacks" by Rebecca Skloot

Vocabulary lists containing spontaneous

Essential Academic Vocabulary for High School Students, List 1

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100 Top "SAT" Words

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Animal Farm

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