- Definitely known or established.
- Fully confident or sure of something.
- Certain to happen or to be the case.
- Excluding no one or nothing; all.
- Determined or fixed, but not specified.
From old french certen, from latin certus "fixed, settled, sure".
- I"m certain that he"s coming.
- It's certain that the weather will be bad tomorrow.
- I'm certain of my answer.
- I"m certain that I"ve met you before.
- I'm certain that I locked the door.