which

pronoun

1. 1

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

   “By now, you must surely know which is which.”

2. 2

   The/Any ones that; whichever.

   “Please take which you please.”

3. 3

   (relative) Introduces a relative clause giving further information about something previously mentioned.

   “He had to leave, which was very difficult.”

4. 4

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