1 decay, decompose, fester, spoil, go bad or off, be tainted, be ruined, mould, moulder, putrefy; corrode, rust, disintegrate, deteriorate, crumble or go or fall to pieces:
When the power went off, all the food in the freezer rotted. The piers holding up the far end of the bridge have all rotted away.
2 waste away, wither away, languish, die, moulder, decline, deteriorate, degenerate, decay, atrophy:
Despite repeated appeals for clemency, he's been rotting away in jail all these years.
3 decay, decomposition, mould, putrefaction, putrescence, blight, corrosion, corruption, disintegration, deterioration:
Once the rot has set in, the job of revitalization can be overwhelming.
4 (stuff and) nonsense, balderdash, rubbish, bunkum, tommy-rot, twaddle, drivel, hogwash, eyewash, trash, Colloq claptrap, bunk, boloney or boloney, bosh, malarkey, moonshine, poppycock, tosh, Slang crap, bull, codswallop, Brit (a load of (old)) cobblers, Taboo balls, bullshit:
He knows nothing whatsoever about linguistics and is just talking a lot of rot.