English definition of “matter”
› a subject or situation that you need to think about or do something about: Could I talk to you about a personal matter? This is a matter of some importance.
› [no plural] In science, matter is the physical substances that exist in the universe.
what’s the matter? A2 used to ask about the reason for a problem: What’s the matter with your leg?
no matter how, what, when, etc. › used to say that something cannot be changed: I never manage to lose any weight, no matter how hard I try.
as a matter of fact › used to say that something is true, especially when it is surprising: As a matter of fact, I used to live near him.