white rust vs fungus

white rust and fungus both are nouns.

Word	Noun	Adjective	Verb	Adverb
white rust	Yes	No	No	No
fungus	Yes	No	No	No

As nouns, fungus is a hypernym of white rust; that is, fungus is a word with a broader meaning than white rust:

white rust: fungus causing a disease characterized by a white powdery mass of conidia
fungus: an organism of the kingdom Fungi lacking chlorophyll and feeding on organic matter; ranging from unicellular or multicellular organisms to spore-bearing syncytia

white rust (noun)	fungus (noun)
fungus causing a disease characterized by a white powdery mass of conidia	an organism of the kingdom Fungi lacking chlorophyll and feeding on organic matter; ranging from unicellular or multicellular organisms to spore-bearing syncytia