which

²which

pronoun

Definition of WHICH

1

: what one or ones out of a group —used as an interrogative <which of those houses do you live in> <which of you want tea and which want lemonade> <he is swimming or canoeing, I don't know which>

2

: whichever <take which you like>

3

—used as a function word to introduce a relative clause ; used in any grammatical relation except that of a possessive ; used especially in reference to animals, inanimate objects, groups, or ideas <the bonds which represent the debt — G. B. Robinson> <the Samnite tribes, which settled south and southeast of Rome — Ernst Pulgram> ; used freely in reference to persons as recently as the 17th century <our Father which art in heaven — Matthew 6:9(Authorized Version)>, and still occasionally so used but usually with some implication of emphasis on the function or role of the person rather than on the person as such <chiefly they wanted husbands, which they got easily — Lynn White> ; used by speakers on all educational levels and by many reputable writers, though disapproved by some grammarians, in reference to an idea expressed by a word or group of words that is not necessarily a noun or noun phrase <he resigned that post, after which he engaged in ranching — Current Biography>

See Usage Discussion at ⁴that

First Known Use of WHICH

before 12th century