which

determiner

1. What, of those mentioned or implied (used interrogatively).

- Which song made the charts?

2. (interrogative) What one or ones (of those mentioned or implied).

- which is bigger?;

3. (relative) The one or ones that.

- show me which one is bigger;

4. (relative) The one or ones mentioned.

- For several seconds he sat in silence, during which time the tea and sandwiches arrived.

- I'm thinking of getting a new car, in which case I'd get a red one.

5. (now dialectal) Used of people (now generally who, whom or that).

noun

1. An occurrence of the word which.

pronoun

1. (relative) Who; whom; what (of those mentioned or implied).

- He walked by a door with a sign, which read: PRIVATE OFFICE.  Their first song, which made the charts in 2004, is great.  We've met some problems, which are very difficult to handle.  He had to leave, which was very difficult.  We have to protect the environment in which we live.  No art can be properly understood apart from the culture of which it is a part.