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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.

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

From Slate • Apr. 3, 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

This type of spontaneous movement has been linked to longevity in other species as well.

From Science Daily • Mar. 26, 2026

They want the gathering to feel casual, spontaneous — the sort of event where everyone simply appears with something charming and the table somehow assembles itself.

From Salon • Mar. 15, 2026

Citra knew it would be healed by morning, but the healing nanites were not spontaneous.

From "Scythe" by Neal Shusterman

From Roget's 21st Century Thesaurus, Third Edition Copyright © 2013 by the Philip Lief Group.