(informal, especially as a question) Used to indicate multiple things are difficult to tell apart

(nonstandard) contraction of which is

Obsolete spelling of which

(interrogative) What, of those mentioned or implied. / The/Any ... that; whichever. / (relative, formal outside certain phrases) Designates the one(s) previously mentioned.

(colloquial, nonstandard, proscribed) Of which; alternative to inanimate sense of “whose”. / Of or pertaining to [some noun phrase ending with] which.

question word to ask about a person's choice

by which

(idiomatic, informal, emphatic) everywhere

(idiomatic) All over; in every direction. / (idiomatic) In all sorts of ways or manners.

(idiomatic) Which point of view is considered or whose interests are used as a basis.