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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

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

From Science Daily • Mar. 26, 2026

The men were accused of working for the U.S. and Israel, though the protests around the country were spontaneous, widespread and came before the current conflict began.

From The Wall Street Journal • Mar. 19, 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

You’d have thought I’d be used to Charlie and his spontaneous weird shit by then, but I wasn’t.

From "Please Ignore Vera Dietz" by A.S. King

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