'which' originates from Old English, specifically the word 'hwilc,' where 'hwa' meant 'who' and 'lic' meant 'like.'

'hwilc' changed from Old English word 'hwilc' and eventually became the modern English word 'which'.

Initially, it meant 'who-like,' but over time it evolved into its current meaning of 'used to refer to one or more people or things from a definite set.'