Used attributively before another noun to denote relation to decay or disease, e.g. 'rot fungus'
Definitionen
Relating to or caused by rot (decay). Rot damage can ruin timber within a few years.
Chiefly British exclamation meaning ‘nonsense; rubbish’
Definitionen
Used to express disbelief, annoyance, or dismissal of something as nonsense. "Rot!" he exclaimed, slamming the book shut.