Emily Dickinson Lexicon

WHICH, pron. [If this is from the Saxon hwilc or hwylc, it is from the Gothic kweleiks, which coincides with the Latin qualis; D. welk, G. welche, welcher, Dan. hwilken, hwilket, Sw. hwilken. This is the probable origin of the word, and its true sense is that of the Latin quis, qualis, quicunque. In these senses it occurs in all Saxon books. Its proper use was as a pronoun of interrogation, “Hwylc man is of eow?” what man is there of you? Matth. vii, 9. “Hwylc is min modor?” who is my mother? Mark iii, 33. Its use for who, Saxon hwa, as in the Lord's prayer, “Our father which art in heaven,” is an improper application of the word. In its original sense it is used for all genders; as, which man, which woman, which thing? As an interrogative we still use it in this manner. Its use for who was of long continuance, but is happily discontinued; and our present practice accords with its original use in the Saxon.]

1. A pronoun or word of interrogation, in all genders; as, which man is it? which woman was it? which is the house?
2. In reference to things, or in the neuter gender, it is a relative referring to something before mentioned; as, “God rested on the seventh day from all his work which he had made.” Gen. ii, 2. In some phrases, the relative may precede the noun to which it refers.
3. Which, like other pronouns, may be used as a substitute for another word or for a sentence. “We are bound to obey all the divine commands, which we can not do without divine aid.” Here which is a substitute for obey all the divine commands. The man was said to be innocent, which he was not. Here which is a substitute for innocent.
4. That which; those which; as, take which you will. The which, by the which, &c. are obsolete.