matter: n. 问题，情况，物质，物品，材料

as a matter of fact

e.g.--I'm sorry, but I can't go with you.

-- What's the matter?

--I have an important matter to deal with.

e.g. This is not a matter of quantity,but a matter of quality.

You mustn't drive a car when you are drunk. It's a matter of life and death.

(2) matter: vi.关系重大，要紧

e.g. 你做什么对我来说都不要紧。

It doesn't matter to me what you do.