sure
Americanadjective
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free from doubt as to the reliability, character, action, etc., of something.
to be sure of one's data.
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confident, as of something expected.
sure of success.
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convinced, fully persuaded, or positive.
to be sure of a person's guilt.
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assured or certain beyond question.
a sure victory.
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worthy of confidence; reliable; stable.
a sure messenger.
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unfailing; never disappointing expectations.
a sure cure.
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unerring; never missing, slipping, etc..
a sure aim.
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admitting of no doubt or question.
sure proof.
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destined; bound inevitably; certain.
sure death.
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Obsolete. secure; safe.
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be sure, to take care (to be or do as specified); be certain.
Be sure to close the windows.
adverb
idioms
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for sure, as a certainty; surely.
It's going to be a good day, for sure.
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make sure, to be or become absolutely certain.
I'm calling to make sure that you remember to come.
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to be sure,
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without doubt; surely; certainly.
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admittedly.
She sings well, to be sure, but she can't act.
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sure enough, as might have been supposed; actually; certainly.
Sure enough, the picnic was rained out.
adjective
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(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
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(foll by of) having no doubt, as of the occurrence of a future state or event
sure of success
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always effective; unfailing
a sure remedy
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reliable in indication or accuracy
a sure criterion
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(of persons) worthy of trust or confidence
a sure friend
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not open to doubt
sure proof
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admitting of no vacillation or doubt
he is very sure in his beliefs
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bound to be or occur; inevitable
victory is sure
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(postpositive) bound inevitably (to be or do something); certain
she is sure to be there tonight
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physically secure or dependable
a sure footing
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obsolete free from exposure to harm or danger
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(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
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without a doubt; surely
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(takes a clause as object) to make certain; ensure
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(foll by of) to establish or confirm power or possession (over)
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informal as might have been confidently expected; definitely: often used as a sentence substitute
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without doubt; certainly
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it has to be acknowledged; admittedly
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adverb
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informal (sentence substitute) willingly; yes
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informal (sentence modifier) without question; certainly
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
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
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
“And then making sure those trees are planted the right way, in the right place and cared for, so that they do survive for decades and decades — it’s really important work.”
From Los Angeles Times • May 23, 2026
"Our legal team says that we have to go for action, that's for sure," Ilicali told BBC Radio Humberside outside Wembley Stadium before kick-off in the final.
From BBC • May 23, 2026
She didn’t tell her family because she wasn’t sure whether the judge would grant her voluntary departure or order her deported.
From The Wall Street Journal • May 23, 2026
“I’m sure those are hard conversations, especially with Attorney General Paxton at the beginning, but he’s willing to have those conversations.”
From Salon • May 23, 2026
“I’ll meet you behind the automotive garage like we planned. You sure they’re not home?”
From "Red Flags and Butterflies" by Sheryl Azzam
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
