word "certain"

Notice
certain of

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certain (adj.)
1. that you can rely on to happen or to be true
- The climbers face certain death if the rescue today is unsuccessful.

* certain (that) ...
- It is certain that they will agree.

* certain to do sth.
- She looks certain to win an Oscar.
- They are certain to agree.

* certain of sth./ of doing sth. 
- If you want to be certain of getting a ticket, book now.

2. firmly believing sth; having no doubts
- She wasn't certain he had seen her.

* certain of/ about sth.
- Are you absolutely certain about this?

* certain who/where, etc...
- I'm not certain who was there.

* To my certain knowledge, he was somewhere else at the time. (= I am sure about it)

3. used to mention a particular thing, person or group without giving any more details about it or them
- For centain personal reasons I shall not be able to attend.
- Certain people might disagree with this.
- They refused to release their hostages unless certain conditions were met.

4. slight; noticeable, but difficult to describe
- That's true, to a certain extent.
- I felt there was a certain coldness (lack of emotion/unfriendliness) in her manner.

certain (pronoun)
* certain of ... (formal) = used for talking about some members of a group of people or things without giving their names
- Certain of those present were unwilling to discuss the matter further.

IDIOMS
* for certain = without doubt
- I can't say for certain when we'll arrive.

* make certain (that...) = to find out whether something is definitely true
- I think there's a bus at 8 but you'd better call to make certain.

* make certain of sth/ of doing sth. = to do sth. in order to be sure that sth. else will happen
- You'll have to leave soon to make certain of getting there on time.

* of a certain age = if you talk about a person being of a certain age, you mean that they are no longer young but not yet old
- The show appeals to an audience of a certain age.

Use
Our city cannot produce certain of fruits and vegetables.
I am certain that her flight will take off at 7pm.
You'd better talk with your friends to make certain that there is a party tonight.
This game can only be played by children in a certain of age.