Webster's Revised Unabridged Dictionary · 1913

Which

Which , pronoun

[Old English which, whilk, Anglo-Saxon hwilc, hwylc, hwelc, from the root of hwā who + līc body; hence properly, of what sort or kind; akin to Old Saxon hwilik which, OFries. hwelik, Dutch welk, German welch, Old High German welīh, hwelīh, Icelandic hvīlīkr, Danish & Swedish hvilken, Gothic hwileiks, hw{not transcribed}leiks; compare Latin qualis. {not transcribed}. See Who, and Like, a., and compare Such.]

1.
Of what sort or kind; what; what a; who. [Obsolete]
And which they weren and of what degree. — Chaucer
2.
A interrogative pronoun, used both substantively and adjectively, and in direct and indirect questions, to ask for, or refer to, an individual person or thing among several of a class; as, which man is it? which woman was it? which is the house? he asked which route he should take; which is best, to live or to die? See the Note under What, pron., 1.
Which of you convinceth me of sin? — John viii. 46
3.
A relative pronoun, used esp. in referring to an antecedent noun or clause, but sometimes with reference to what is specified or implied in a sentence, or to a following noun or clause (generally involving a reference, however, to something which has preceded). It is used in all numbers and genders, and was formerly used of persons.
And when thou fail'st -- as God forbid the hour! -- Must Edward fall, which peril heaven forfend! — Shakespeare
God... rested on the seventh day from all his work which he had made. — Gen. ii. 2
Our Father, which art in heaven. — Matt. vi. 9
The temple of God is holy, which temple ye are. — 1 Cor. iii. 17
4.
A compound relative or indefinite pronoun, standing for any one which, whichever, that which, those which, the... which, and the like; as, take which you will.
Do not they blaspheme that worthy name by the which ye are called? — James ii. 7

The which was formerly often used for which. The expressions which that, which as, were also sometimes used by way of emphasis.

Which, referring to a series of preceding sentences, or members of a sentence, may have all joined to it adjectively. “All which, as a method of a proclamation, is very convenient.” Carlyle.