sure

American  

[shoor, shur] / ʃʊər, ʃɜr /

adjective

surer, comparative surest superlative

1. free from doubt as to the reliability, character, action, etc., of something.

   to be sure of one's data.

2. confident, as of something expected.

   sure of success.

3. convinced, fully persuaded, or positive.

   to be sure of a person's guilt.

4. assured or certain beyond question.

   a sure victory.

5. worthy of confidence; reliable; stable.

   a sure messenger.

6. unfailing; never disappointing expectations.

   a sure cure.

7. unerring; never missing, slipping, etc..

   a sure aim.

8. admitting of no doubt or question.

   sure proof.

9. destined; bound inevitably; certain.

   sure death.

10. Obsolete. secure; safe.

11. be sure, to take care (to be or do as specified); be certain.

    Be sure to close the windows.

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adverb

1. Informal. certainly; surely.

   It sure is cold out. Sure, I'll come.

idioms

1. for sure, as a certainty; surely.

   It's going to be a good day, for sure.

2. make sure, to be or become absolutely certain.

   I'm calling to make sure that you remember to come.

3. to be sure,

   1. without doubt; surely; certainly.

   2. admittedly.

      She sings well, to be sure, but she can't act.

4. sure enough, as might have been supposed; actually; certainly.

   Sure enough, the picnic was rained out.

sure British  

/ ʃɔː, ʃʊə /

adjective

1. (sometimes foll by of) free from hesitancy or uncertainty (with regard to a belief, conviction, etc)

   we are sure of the accuracy of the data

   I am sure that he is lying

2. (foll by of) having no doubt, as of the occurrence of a future state or event

   sure of success

3. always effective; unfailing

   a sure remedy

4. reliable in indication or accuracy

   a sure criterion

5. (of persons) worthy of trust or confidence

   a sure friend

6. not open to doubt

   sure proof

7. admitting of no vacillation or doubt

   he is very sure in his beliefs

8. bound to be or occur; inevitable

   victory is sure

9. (postpositive) bound inevitably (to be or do something); certain

   she is sure to be there tonight

10. physically secure or dependable

    a sure footing

11. obsolete free from exposure to harm or danger

12. (usually imperative or dependent imperative; takes a clause as object or an infinitive, sometimes with to replaced by and) to be careful or certain

    be sure and shut the door

    I told him to be sure to shut the door

13. without a doubt; surely

14. 1. (takes a clause as object) to make certain; ensure

    2. (foll by of) to establish or confirm power or possession (over)

15. informal as might have been confidently expected; definitely: often used as a sentence substitute

16. 1. without doubt; certainly

    2. it has to be acknowledged; admittedly

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adverb

1. informal (sentence substitute) willingly; yes

2. informal (sentence modifier) without question; certainly

sure More Idioms  

More idioms and phrases containing sure

• for certain (sure)
• make sure
• slow but sure
• to be sure

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Usage

What are other ways to say sure?

Someone who is sure of something is free from doubt about its reliability or character. How does sure compare to synonyms certain, confident, or positive? Learn more on Thesaurus.com. 

Commonly Confused

Both sure and surely are used as intensifying adverbs with the sense “undoubtedly, certainly.” In this use, sure is generally informal and occurs mainly in speech and written representations of speech: She sure dazzled the audience with her acceptance speech. It was sure hot enough in the auditorium. Surely is used in this sense in all varieties of speech and writing, even the most formal: The court ruled that the law was surely meant to apply to both profit-making and nonprofit organizations. See also quick, slow.

Other Word Forms

Derived Forms

• oversureness
  noun
• sureness
  noun
• unsureness
  noun
• oversure
  adjective
• unsure
  adjective
• oversurely
  adverb
• unsurely
  adverb

Inflected Forms

Adjectives

• surer
  comparative
• surest
  superlative

Etymology

Origin of sure

First recorded in 1300–50; Middle English sur(e), from Middle French sur, Old French seur, from Latin sēcūrus “carefree”; see secure

Explanation

Being sure has to do with being certain, convinced, trustworthy, or dependable. You can trust a sure thing. Besides being a synonym for yes, sure has to do with lots of kinds of dependability. If you have a sure eye, then you have good aim, maybe with shooting a basketball or throwing darts. If you're sure of yourself, you're confident. A sure thing or sure bet is something almost certain to happen. If you're 100% convinced of something, you're sure of it.

Example Sentences

See Examples For:

sure surer surest

Wall Street bankers have told clients they aren’t sure the interest rates will ease soon—an issue that has big AI companies reassessing their estimates for how much the infrastructure build-out will cost.

From The Wall Street Journal ● Jul. 28, 2026

His goal is “making sure that the 9th district has representation that actually fights for it.”

From Los Angeles Times ● Jul. 28, 2026

Handed a way out by the club she represented as a junior, she says she was not sure what to expect when signing for Renee Slegers' side.

From BBC ● Jul. 28, 2026

To make sure Europeans immediately know whether the online content they see is real or fake.

From Barron's ● Jul. 28, 2026

I’m not sure how I expected her to react, but it wasn’t with a big smile.

From "Split the Sky" by Marie Arnold

Round after round, the Hurricanes have knocked off teams that seemed surer bets to make the championship.

From The Wall Street Journal ● Jan. 9, 2026

A surer indicator is to observe what’s popular in the current marketplace.

From Salon ● Jun. 1, 2025

The closer the algorithm puts a specific chart toward the tip of an arm, the surer it is of its decision, while those placed closer to the central body are less certain.

From Science Daily ● May 29, 2024

But I’m now surer of the impression I had of him after we first talked.

From Los Angeles Times ● Feb. 27, 2024

His weakness, his distress, only made me surer.

From "Anthem of a Reluctant Prophet" by Joanne Proulx

That’s high-risk, but it is the surest way of removing the fuel for a nuclear weapon.

From The Wall Street Journal ● Jun. 10, 2026

Who knows if Mr. Musk will every colonize Mars, but the surest bet is never to bet against American innovation.

From The Wall Street Journal ● May 21, 2026

The surest sign of market dislocation is when banks start quantifying their exposure to a given issue.

From MarketWatch ● Feb. 24, 2026

Players might however make a calculated decision on which nation offers the surest path to the Test stage.

From BBC ● Feb. 13, 2026

It was a vintage Franklin performance, reminiscent of his bemused but devastating recommendations to the English government in 1770 about the surest means to take the decisive action guaranteed to destroy the British Empire.

From "Founding Brothers: The Revolutionary Generation" by Joseph J. Ellis

Related Words

• assured
• clear
• confident
• convinced
• positive