which

Etymology

From Middle English which, hwic, wilche, hwilch, whilk, hwilc, from Old English hwelċ (“which”), from Proto-Germanic *hwilīkaz (“what kind”, literally “like what”), derived from *hwaz, equivalent to who + like. Cognates include Scots whilk (“which”), West Frisian hokker (“which”), Dutch welk (“which”), Low German welk (“which”), German welcher (“which”), Danish hvilken (“which”), Swedish vilken (“which”), Norwegian hvilken (“which”), Icelandic hvílíkur (“which”).

det

1. (interrogative) What, of those mentioned or implied.
   Which song shall we play?
   They couldn't decide which song to play.
   Which one is bigger?
   Show me which one is bigger.
2. The/Any ... that; whichever.
   You may go which way you please.
3. (relative, formal outside certain phrases) Designates the one(s) previously mentioned.
   After glaring upon the smoking philosopher, who took his misfortunes with such positive nonchalance, he growled out an oath in German, which language is particularly adapted for growling in; then, raising his hand, he dealt him a blow on his pipe, which sent it, like a rocket, into the midst of the players. 1860, Alfred Henry Forrester, Fairy footsteps, or, Lessons from legends, with illustr., by Alfred Crowquill, page 166 (Google Books view)
   Whitaker’s blog post, housed on a website called Minutes Before Six, goes on to make references to Albert Camus’ 1947 classic, The Plague, dips into a Camus-inspired existential ramble and returns to an attempt to convey the detail of Prieto’s being essentially “noble,” which fact, he admits, will be lost in translation to anyone unfamiliar with death row units. January 21, 2015, Texas Public Radio, “Voices From Death Row: A Prisoner Writes An Ode To ‘Living Dyingly’”, in Texas Public Radio
   All the phones come in plastic bodies that have been given a brushed-metal finish and carry 64-bit processors from Intel, which fact they proudly announce with an Intel Inside logo on the back. May 2, 2015, Adarsh Matham, “Battle of the Smartphones”, in The New Indian Express
   He once owned a painting of the house, which painting would later be stolen.
   Yesterday, I met three men with long beards, which men I remember vividly.
   For several seconds he sat in silence, during which time the tea and sandwiches arrived.
   I'm thinking of getting a new car, in which case I'd get a red one.

pron

1. (interrogative) What one or ones (of those mentioned or implied).
   Which is which?
   By now, you must surely know which is which.
   Which is bigger, the red one or the blue one?
   I'm unable to determine which is bigger.
   Which of these do you want to keep?
   Which of these banes of modern business life is worse remains open to debate. But what is clear is that office workers are on a treadmill of pointless activity. Managers allow meetings to drag on for hours. Workers generate e-mails because it requires little effort and no thought. An entire management industry exists to spin the treadmill ever faster. 2013-08-17, Schumpeter, “In praise of laziness”, in The Economist, volume 408, number 8849
2. The/Any ones that; whichever.
   Please take which you please.
3. (relative) Introduces a relative clause giving further information about something previously mentioned.
   He walked by a door with a sign, which read: PRIVATE OFFICE.
   I found my camera, which I thought I'd lost, under the bed.
   No art can be properly understood apart from the culture of which it is a part.
   He had to leave, which was very difficult.
   Many genes with reproductive roles also have antibacterial and immune functions, which indicate that the threat of microbial attack on the sperm or egg may be a major influence on rapid evolution during reproduction. 2013 May-June, Katrina G. Claw, “Rapid Evolution in Eggs and Sperm”, in American Scientist, volume 101, number 3
   Plastics are energy-rich substances, which is why many of them burn so readily. Any organism that could unlock and use that energy would do well in the Anthropocene. Terrestrial bacteria and fungi which can manage this trick are already familiar to experts in the field. 2013-07-20, “Welcome to the plastisphere”, in The Economist, volume 408, number 8845
4. (relative, chiefly archaic) Used of people (now generally who, whom, that; which remains possible with words also referred to by it like baby, child).