Origin and history of feed

past-participle adjective from feed (v.). Fed up "surfeited, disgusted, bored," is British slang first recorded 1900 (some early uses connect it to the Boer War), extended to U.S. by World War I; probably from earlier phrases like fed up to the back teeth. Earlier it was used of livestock, "fatten up by feeding." The notion probably is the same one in to have had enough "to have had too much."

1920, in the electronics sense, "the return of a fraction of an output signal to the input of an earlier stage," from verbal phrase, from feed (v.) + back (adv.). Transferred use, "information about the results of a process" is attested by 1955.