1. (pron.)which what one?: Which of these do you want? Which do you want?
2. which whichever: Choose which appeals to you.
3. which (used relatively in restrictive and nonrestrictive clauses to represent a specified antecedent): This book, which I read last night, was exciting. The socialism which Owen preached was unpalatable to many. The lawyer represented five families, of which ours was the largest.
4. which (used relatively in restrictive clauses having that as the antecedent): Damaged goods constituted part of that which was sold at the auction.
5. which (used after a preposition to represent a specified antecedent): the house in which I lived.
6. which (used relatively to represent a specified or implied antecedent) the one that; a particular one that: You may choose which you like.
7. which (used in parenthetic clauses) the thing or fact that: He hung around for hours and, which was worse, kept me from doing my work.
8. (adj.)which what one of (a certain number or group mentioned or implied)?: Which book do you want?
9. which whichever; any that: Go which way you please, you'll end up here.
10. which being previously mentioned: It rained all day, during which time we played cards.
Etymology: (bef. 900; ME; OE hwilc, hwelc=hwe- (akin to hwāwho ) +-līc body, shape, kind; c. OS (h)wilik, OHG hwelīk, ON hvīlīkr, Go hwileiks lit., of what form)
1. (determiner)which used to specify a possible choice Which dress should I wear?; Which employee has been chosen this year?
2. which indicates sth just mentioned He started yelling, at which point I decided to leave.
3. (pronoun)which used to specify a possible choice Which of the two dresses should I wear?; There are so many good paintings. Which is the winner?
4. which indicates sth that has just been mentioned The car, which I just bought, is being repaired.; Then he made a funny face, which was funny.
Definition of 'which'
Webster Dictionary
1. (adj)which of what sort or kind; what; what a; who
2. (adj)which 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
3. which 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
4. which 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
Sense: used in questions etc when asking someone to point out, state etc one or more persons, things etc from a particular known group Which (colour) do you like best?; Which route will you travel by?; At which station should I change trains?; Which of the two girls do you like better?; Tell me which books you would like; Let me know which train you'll be arriving on; I can't decide which to choose.
Definitions of which 
Afrikaans: watter
Arabic: أي
Bulgarian: кой
Brazilian: qual
Czech: jaký, který, co
German: welche
Danish: hvilken
Greek: ποιος (απ' όλους)
Spanish: cuál
Estonian: missugune, mis, kumb
Farsi: کدام
Finnish: mitä, kuka, kumpi
French: quel; lequel, laquelle
Hebrew: אֵיזֶה
Hindi: कौन, कौन सा
Croatian: koji
Hungarian: melyik(et)?
Indonesian: yang mana
Icelandic: hver, hvor, hvaða
Italian: quale; chi
Japanese: どちら
Korean: (일정수의 물건, 일, 사람 가운데) 어느 쪽
Lithuanian: kuris
Latvian: kurš
Malay: yang mana satu
Dutch: welk
Norwegian: hvilken; hvem, hva
Polish: który
Portuguese: qual
Romanian: care; pe care; la care
Russian: какой; который
Slovak: aký, ktorý, čo
Slovenian: kateri
Serbian: koji
Swedish: vilken, vilket, vilka, ve
Thai: อันไหน; สิ่งไหน
Turkish: hangisi(ni), hangi
Taiwanese: 哪一個
Ukrainian: котрий, який
Urdu: کون سا
Vietnamese: cái nào; người nào
Chinese: 哪一个
