certain
Americanadjective
-
free from doubt or reservation; confident; sure.
I am certain he will come.
- Synonyms:
- satisfied
-
destined; sure to happen (usually followed by an infinitive).
He is certain to be there.
-
inevitable; bound to come.
They realized then that war was certain.
-
established as true or sure; unquestionable; indisputable.
It is certain that he tried.
- Synonyms:
- clear, plain, obvious, incontrovertible, irrefutable, incontestable, indubitable
-
fixed; agreed upon; settled.
on a certain day; for a certain amount.
- Synonyms:
- determined
-
definite or particular, but not named or specified.
A certain person phoned. He had a certain charm.
-
that may be depended on; trustworthy; unfailing; reliable.
His aim was certain.
-
some though not much.
a certain reluctance.
-
Obsolete. steadfast.
pronoun
idioms
adjective
-
(postpositive) positive and confident about the truth of something; convinced
I am certain that he wrote a book
-
(usually postpositive) definitely known
it is certain that they were on the bus
-
(usually postpositive) sure; bound; destined
he was certain to fail
-
decided or settled upon; fixed
the date is already certain for the invasion
-
unfailing; reliable
his judgment is certain
-
moderate or minimum
to a certain extent
-
to ensure (that one will get something); confirm
adverb
determiner
-
-
known but not specified or named
certain people may doubt this
-
( as pronoun; functioning as plural )
certain of the members have not paid their subscriptions
-
-
named but not known
he had written to a certain Mrs Smith
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."
Vocabulary lists containing certain
The Real Deal: Synonyms for "True"
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List 1
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A Sure Thing: Synonyms for "Definite"
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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.
Starting in the 1980s, the Chinese central government targeted becoming a scientific superpower in certain technologies, including biotech.
From The Wall Street Journal • Apr. 11, 2026
Benesh says the date that most Big Food companies are planning to phase out certain dyes isn’t a coincidence.
From Salon • Apr. 11, 2026
Researchers led by Flinders University, working with international collaborators, have uncovered how a rare blood clotting condition can develop after certain COVID19 adenovirus-based vaccines or even after a natural adenovirus infection.
From Science Daily • Apr. 10, 2026
Whether or not concerns over artificial-intelligence disruption have been blown out of proportion, one thing is certain: The pressure on the industry shows no sign of abating.
From Barron's • Apr. 10, 2026
She’d always tell us that we were only going to buy a certain number of tickets, and once they were gone, that was it.
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.
