before 900; Middle English; Old English hwilc, hwelc, equivalent to hwe- (base of hwā who) + -līc body, shape, kind (see like¹); cognate with Old Frisian hwelik, Dutch welk, German welch, Gothic hwileiks literally, of what form

The relative pronoun which refers to inanimate things and to animals: The house, which we had seen only from a distance, impressed us even more as we approached. The horses which pulled the coach were bay geldings. Formerly, which referred to persons, but this use, while still heard ( a man which I know ), is nonstandard. Contrary to the teachings of some usage guides, which introduces both restrictive and nonrestrictive clauses. The “rule” that which can be used only with nonrestrictive clauses has no basis in fact. In edited prose three-fourths of the clauses in which which is the relative pronoun are restrictive: A novel which he later wrote quickly became a bestseller. See also that.