(n.) A minute mold or fungus forming reddish or rusty spots on the leaves and stems of cereal and other grasses (Trichobasis Rubigo-vera), now usually believed to be a form or condition of the corn mildew (Puccinia graminis). As rust, it has solitary reddish spores; as corn mildew, the spores are double and blackish.
RUST
Meaning of RUST in English
Webster's English dictionary. Английский словарь Webster. 2012