NO DOUBT[never before noun]›completely sure of something, or knowing without doubt that something is true: [+ (that)]I feel absolutely certain that you're doing the right thing.[+ question word]Nobody was certain how the accident had happened.He was quite certain about/of the thief's identity. → Oppositeuncertain
know/say for certain›to know something without doubt: We don't know for certain whether she's coming.
SURE TO HAPPEN›sure to happen, to do something, or to be true: [+ (that)]It now looks certain that she will resign.[+ to do sth]She is certain to do well in the exams.How can we make certain that (= do something to be sure that) she sees the note?One thing is certain. Her attacker knew where she lived.
PARTICULAR[always before noun]›used to refer to a particular person or thing without naming or describing them exactly: The museum is only open at certain times of the day.Certain people react badly to these drugs.
a certain›used before a noun to mean existing, but difficult to describe the exact quality or amount: He's got a certain charm.You have to have a certain amount of courage to perform in public.
certain offormal›used to refer to some of a group of people or things: Certain of you already know the news.