Middle English roten, from Old English rotian, of animal substances, "to decay, putrefy, undergo natural decomposition" (intransitive), also of vegetable matter," from Proto-Germanic *rutjan (source also of Old Saxon roton, Old Norse rotna, Old Frisian rotia, Middle Dutch roten, Dutch rotten, Old High German rozzen "to rot," German rößen "to steep flax"), from stem *rut-. Related: Rotted; rotting.
By c. 1200 as "fester or decay morally, become morally corrupt." Transitive sense of "cause decomposition in" is from late 14c. To rot in prison (mid-14c.) suggests wasting disease.
early 14c., "decay, corruption, putrefaction," from rot (v.) or of Scandinavian origin (compare Icelandic rot, Swedish röta, Danish røde "decay, putrefaction"), or both, in any case from the root of the verb. From c. 1400 as the name of a disease in sheep, also generally, "condition of rottenness in a plant or animal, process or state of being rotten." Slang sense of "rubbish, trash" is from 1848.