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

“I’m going to learn from them and move on, and next week be able to learn from it and make sure it doesn’t happen again.”

From Los Angeles Times ● Aug. 14, 2026

To be sure, there are pitfalls to plan for like the “kiddie tax,” whereby unearned income above a certain amount is taxed at the parents’ rate.

From MarketWatch ● Aug. 14, 2026

Asma, who is 13, wants to become a doctor and is sure someday she will be.

From BBC ● Aug. 14, 2026

We want to make sure we are there when they are ready to book because those companies are not going to take on the responsibility of actually doing the bookings.

From The Wall Street Journal ● Aug. 14, 2026

“Try not to worry. I’m sure Grandma Sadie’s gonna find a way to help you make this choice.”

From "Split the Sky" by Marie Arnold

A surer bet, Lopez told listeners, is to buy a franchise like a McDonald’s or Taco Bell.

From The Wall Street Journal ● Feb. 10, 2026

If they even had a sliver of doubt before the Munich showdown against PSG they will be even surer now.

From BBC ● May 31, 2025

That is, provided that person doesn't simply resort to a surer thing.

From Salon ● Dec. 6, 2024

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

All of this delighted Papa, filled him with pride for his son who had returned a larger man, with a surer sense of himself and of where we all had come from.

From "Farewell to Manzanar" by Jeanne Houston

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

Refusing to be drawn into operational details, Miliband reiterated that "ending the conflict is the best and surest way to get the strait reopened".

From BBC ● Mar. 17, 2026

The surest way to snag great travel tips and become overwhelmed and riled up all at once while planning a vacation?

From The Wall Street Journal ● Feb. 25, 2026

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

From MarketWatch ● Feb. 24, 2026

All his life, he’d wanted to be a part of this brotherhood, because he thought it would be the surest way to prove to himself and to his people that he was a man.

From "Beasts of Prey" by Ayana Gray

Related Words

• assured
• clear
• confident
• convinced
• positive