Meaning

adjective very bad

adjective damaged by decay; hence unsound and useless

adjective having decayed or disintegrated; usually implies foulness

originFrom Middle English roten, from Old Norse rotinn (“decayed, rotten”), past participle of an unrecorded verb related to Old Norse rotna (“to rot”) and Old English rotian (“to rot”), ultimately from Proto-Germanic *rutāną (“to rot”). See rot. By surface analysis, rot + -en (past participle).

Etymology from Wiktionary, CC BY-SA 3.0