Etymologically, the word is a diminutive form of *roch, from Germanic *hrokk (meaning ‘overgarment’). However, the word is not attested without its diminutive suffix in Anglo-Norman or Continental French (unless plural forms such as rochés, rochesz, rochez and rochis can be interpreted as such).

The shift in sense from ‘overgarment’ to ‘undergarment’ (sense 2, glossing Latin perizoma) is unetymological but can also be found in Middle English (MED roket n.1 (e)).