certain

American  

[sur-tn] / ˈsɜr tn /

adjective

1. free from doubt or reservation; confident; sure.

   I am certain he will come.

   Synonyms:

   satisfied

2. destined; sure to happen (usually followed by an infinitive).

   He is certain to be there.

3. inevitable; bound to come.

   They realized then that war was certain.

4. established as true or sure; unquestionable; indisputable.

   It is certain that he tried.

   Synonyms:

   clear, plain, obvious, incontrovertible, irrefutable, incontestable, indubitable

5. fixed; agreed upon; settled.

   on a certain day; for a certain amount.

   Synonyms:

   determined

6. definite or particular, but not named or specified.

   A certain person phoned. He had a certain charm.

7. that may be depended on; trustworthy; unfailing; reliable.

   His aim was certain.

8. some though not much.

   a certain reluctance.

9. Obsolete. steadfast.

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pronoun

1. certain ones.

   Certain of the members declined the invitation.

idioms

1. for certain, without a doubt; surely.

   I know for certain that I have seen that face before.

certain British  

/ ˈsɜːtən /

adjective

1. (postpositive) positive and confident about the truth of something; convinced

   I am certain that he wrote a book

2. (usually postpositive) definitely known

   it is certain that they were on the bus

3. (usually postpositive) sure; bound; destined

   he was certain to fail

4. decided or settled upon; fixed

   the date is already certain for the invasion

5. unfailing; reliable

   his judgment is certain

6. moderate or minimum

   to a certain extent

7. to ensure (that one will get something); confirm

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adverb

1. definitely; without a doubt

   he will win for certain

determiner

1. 1. known but not specified or named

      certain people may doubt this

   2. ( as pronoun; functioning as plural )

      certain of the members have not paid their subscriptions

2. named but not known

   he had written to a certain Mrs Smith

certain More Idioms  

1. see for certain.

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Usage

What are other ways to say certain? Someone who is certain of something is free from doubt or reservation about it. How is certain different from sure, confident, and positive? Find out on Thesaurus.com.

Etymology

Origin of certain

First recorded in 1250–1300; Middle English, from Old French, from Vulgar Latin certānus (unrecorded), from Latin cert(us) “sure, settled” (adjective use of past participle of cernere “to decide, separate, sift”) + -ānus -an

Explanation

When you're certain, you're sure about something. When you raise your hand to give the answer, you feel certain that you are correct. Certain can mean "definite" or "sure to happen," like getting wet, a certain outcome of not having an umbrella in a rainstorm. It can also refer to a particular person or thing. You can use it avoid explaining something unnecessarily — you might say, "There are certain things I want to do when I get home." To avoid saying someone's name, you can say, "a certain person," as in, "A certain person left the kitchen a mess."

Example Sentences

Matarazzo couldn’t shake what he called “a drive to fulfill a certain curiosity that I had growing up.”

From The Wall Street Journal • Apr. 18, 2026

“These models know a huge amount about the inside of a certain building, and so on and so forth,” Stewart said.

From MarketWatch • Apr. 18, 2026

Vaccination is also urged for people who have an occupational risk for exposure, such as certain lab workers.

From Los Angeles Times • Apr. 18, 2026

Expedition 33 is set in a world where a supernatural being known as The Paintress prevents the population from growing past a certain age.

From BBC • Apr. 17, 2026

But as a rule, Clare never sent a wandering spirit to this particular realm unless he was absolutely, positively, most certainly certain.

From "The Undead Fox of Deadwood Forest" by Aubrey Hartman

Related Words

• absolute
• clear
• definite
• genuine
• positive
• real
• safe
• sure
• true
• undeniable