Definition of: which

(hwich) pron. & adjective
1. Interrogatively, what individual person or thing, or group of persons or things collectively, of a certain number or class: asking for the indication or definite description. In this sense which is used both substantively and adjectively, singular and plural: Which shall I take? Which apple do you want? Which mammals are carnivorous?
2. As a relative pronoun, that particular one or ones of a certain number or class of impersonal beings or things: pointing out or definitely fixing upon that which is designated in the antecedent word, phrase, or clause to which it is related: now generally as a substantive, but sometimes as an adjective: He raised his hand, which gesture attracted my attention. Which as a relative now refers only to animals, without distinction of masculine or feminine, or to things without life; it was formerly used for persons, even in the most exalted sense, as “Our Father, which art in heaven.”
3. Also relatively, the one that: often equivalent to the use of the interrogative in a dependent question: used substantively or adjectivally: Tell me which (or which apple) you prefer. [OE hwelc, hwilc]