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.

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

From Science Daily • May 10, 2026

In 2024, for example, more than 700 newborns died from spontaneous bleeding in their brains, which could have been complicated by liver disease or prematurity.

From Salon • May 7, 2026

Shapiro wants to bring back the spontaneous phone call.

From The Wall Street Journal • May 1, 2026

That moment came courtesy of a guy wearing a Cubs uniform, but Monday grew up in Santa Monica and delivered his spontaneous commemoration of Flag Day in the year of America’s bicentennial.

From Los Angeles Times • Apr. 19, 2026

Not many institutions can produce this spontaneous music at will, summer after summer, year after year.

From "The Lives of a Cell" by Lewis Thomas

Vocabulary lists containing spontaneous

Essential Academic Vocabulary for High School Students, List 1

Looking to grow your vocabulary? Check out this interactive, curated word list from our team of English language specialists at Vocabulary.com – one of over 17,000 lists we've built to help learners worldwide!

100 Top "SAT" Words

Interested in learning more words like this one? Our team at Vocabulary.com has got you covered! You can review flashcards, quiz yourself, practice spelling, and more – and it's all completely free to use!

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!