'inch' originates from Old English, specifically the word 'ynce' (also spelled 'ynċe'), borrowed from Latin 'uncia', where 'uncia' meant 'one-twelfth' (a twelfth part).

'uncia' (Latin) passed into Old English as 'ynce'/'ynċe', then into Middle English as 'ince'/'ynche', and eventually became the modern English word 'inch'.

Initially, it meant 'a twelfth part' (of a foot) as in Latin 'uncia'; over time it evolved into the specific unit of length now defined as exactly 2.54 centimetres.