"fungal decay in timber," by 1779, from dry (adj.) + rot (n.). Figurative sense of "concealed or unsuspected inward degeneration" is by 1821.

1884, from tommy in sense of "a simpleton" (1829), diminutive of Tom (as in tom-fool) + rot (n.).

"to soak stems of fibrous plants (flax, hemp, jute, etc.) to soften them," mid-15c., probably from Middle Dutch roten (or an unrecorded cognate Old Norse word that is related to Norwegian røyta, Swedish röta, Danish røde); the group is considered to be related to Old English rotian "to rot" (see rot (v.)), but the vowel is difficult. The process partially rots the stems so the workers may better get the fibers.

also rot-gut, "unwholesome liquor; cheap, adulterated whiskey," 1630s, from rot (v.) + gut (n.).

c. 1300, roten, of animal substances, "in a state of decomposition or putrefaction," from a Scandinavian source akin to Old Norse rotinn "decayed," past participle of verb related to rotna "to decay," from Proto-Germanic stem *rut- (see rot (v.)).

Of vegetable substances from late 14c. Also used in North America of weak, melting ice (1660s). The figurative sense of "morally corrupt, wicked; unsound in character or quality" is from late 14c.; the weakened slang sense of "bad" is recorded by 1880.

Rotten apple is from a saying traced back to at least 1528: "For one rotten apple lytell and lytell putrifieth an whole heape." The Rotten Row in London and elsewhere probably is from a different word, but one of uncertain origin. Rotten-hearted is attested by late 14c.

"person deemed objectionable on moral grounds," 1889, slang, from rot (v.) + -er (3).