Английский Этимологический словарь - fret (v.)

- O.E. fretan "eat, devour" (in M.E., used of animals' eating), from P.Gmc. compound *fra- "for-" + *etan "to eat." Figurative sense of "irritate, worry, eat one's heart out" is c.1200. Modern Ger. still distinguishes essen for humans and fressen for animals.