fretyoudaoicibaDictYouDict[fret 词源字典]
fret: English has three separate words fret. Fret ‘irritate, distress’ [OE] goes back to a prehistoric Germanic compound verb formed from the intensive prefix *fra- and the verb *etan (ancestor of English eat), which meant ‘eat up, devour’. Its modern Germanic descendants include German fressen ‘eat’ (used of animals). In Old English, it gave fretan, which also meant ‘devour’, but this literal meaning had died out by the early 15th century, leaving the figurative ‘gnaw at, worry, distress’. Fret ‘decorate with interlaced or pierced design’ [14] (now usually encountered only in fretted, fretwork, and fretsaw) comes from Old French freter, a derivative of frete ‘trellis, embossed or interlaced work’, whose origins are obscure.

Also lost in the mists of time are the antecedents of fret ‘ridge across the fingerboard of a guitar’ [16].
=> eat[fret etymology, fret origin, 英语词源]