We have every reason to refuse.我们完全有理由拒绝。

Can you tell me the reason why you were late this morning.你能告诉我今早为什么迟到。

reason是理由和原因的意思。再来一个例子：

We have reason to believe that he was lying.我们有理由相信他是在撒谎。

reason也可表示道理，情理。

Why didn't you listen to reason?你为什么不愿听从道理?

reason也可做动词，表示讲理，和某人讲理就用介词with.

There is no use reasoning with him.和他讲理根本没用。