- whichW1S1 [wıtʃ] determiner, pron[: Old English; Origin: hwilc]1.) used to ask or talk about one or more members of a group of people or things, when you are uncertain about it or about them▪ Which book are you looking for?▪ Which are the most important crops?▪ Miranda was sure it was one of them, but was not sure which.which of▪ I don't know which of us was the more scared.2.) used after a noun to show what thing or things you mean▪ Did you see the letter which came today?▪ Now they were driving by the houses which Andy had described.3.) used, after a ↑comma in writing, to add more information about the thing, situation, or event you have just mentioned▪ The house, which was completed in 1856, was famous for its huge marble staircase.▪ One of the boys kept laughing, which annoyed Jane intensely.▪ He was educated at the local grammar school, after which he went on to Cambridge.▪ She may have missed the train, in which case (=if this happens) she won't arrive for another hour.4.) don't know/can't tell etc which is whichif you do not know which is which, you cannot see the difference between two very similar people or things▪ The twins are so alike I can never tell which is which.▬▬▬▬▬▬▬HINT sense 2In informal and spoken English, it is more usual to use that : This is the one that I wanted.▬▬▬▬▬▬▬
Dictionary of contemporary English. 2013.