"be peevish or worried," early 12c., from Old English fretan "eat, devour" (in Old English used of monsters and Vikings; in Middle English used of animals' eating), from Proto-Germanic compound *fra- "for-" + *etan "to eat" (cf. Dutch vreton, Old High German freggan, German fressen, Gothic fraitan). Transitive sense of "eat away" is from late 12c. Figurative sense of "irritate, worry, eat one's heart out" is c.1200. Modern German still distinguishes essen for humans and fressen for animals. Related: Fretted; fretting. As a noun, from early 15c.