1 a certain thing, person, place etc is a particular thing, person etc that you are not naming or describing exactly: You can get cheaper fares on certain days of the year. | There are certain things I just can't discuss with my mother. | certain of formal (=several particular people or things in a group): Certain of the older members objected strongly to the proposal.2 some, but not a lot: a certain amount of: a certain amount of flexibility | to a certain extent/degree (=in a limited way, but not completely): I agree with you to a certain extent but there are other factors to consider.3 a certaina) enough of a particular quality to be noticed: There's a certain prestige about going to a private school.b) formal used to talk about someone you do not know but whose name you have been told: There's a certain Mrs. Myles on the phone for you..2 adjective1 (not before noun) confident and sure, without any doubts: Just so we're absolutely certain, can I check these figures? | certain (that): We're certain that by tomorrow, Mr Knowles, you'll have an answer. | certain who/what/how etc: I'm not certain whether there's a bus service on Sundays.(+ about/of): Now are you certain about that? | I'm not quite certain of how much is left in that account.2 know/say for certain to know something without any doubt: "How much will the repairs cost." "I couldn't say for certain."3 make certaina) to do something in order to be sure that something will happen: make certain (that): Can you draw Harry a map just to make certain he'll find the hotel?b) to check that something is correct or true(+ of): I suggest you make certain of your facts before you accuse anybody.4 if something is certain, it will definitely happen or is definitely true: a business facing certain bankruptcy | it is certain (that): It now seems certain that Pam will lose her license. | certain to do sth: There's one boy who's certain to succeed! | it is not certain who/what/how etc: It's not certain where he lived. (=no one knows definitely)
Longman dictionary of contemporary English. 2004.