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.

Most cancers are spontaneous and can’t be detected in a genetic test.

From Barron's • May 21, 2026

They also showed stronger protection against spontaneous tumors and chemically induced skin cancer.

From Science Daily • May 10, 2026

“She had a spontaneous unexplained brain bleed that led to brain death.”

From Salon • May 7, 2026

I’m batting about .500 in my attempt to revive the spontaneous call.

From The Wall Street Journal • May 1, 2026

This hasn’t stopped some believers—physicists included—from picketing high-energy laboratories like Fermilab; they believe that a high-energy collision could cause a spontaneous collapse of the vacuum.

From "Zero: The Biography of a Dangerous Idea" by Charles Seife

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

Want to remember this word for good? Start your learning journey today with our library of interactive, themed word lists built by the experts at Vocabulary.com – we'll help you make the most of your study time!