Which  —interrog. Adj. Asking for choice from a definite set of alternatives (which john do you mean?; say which book you prefer). —rel. Adj. Being the one just referred to; and this or these (ten years, during which time they admitted nothing). —interrog. Pron. 1 which person or persons? (which of you is responsible?). 2 which thing or things? (say which you prefer). —rel. Pron. (poss. Of which, whose) 1 which thing or things, usu. Introducing a clause not essential for identification (the house, which is empty, has been damaged). 2 used in place of that after in or that (there is the house in which i was born; that which you have just seen). [old english]