mildew vs spoilage

mildew and spoilage both are nouns.

Word	Noun	Adjective	Verb	Adverb
mildew	Yes	No	Yes	No
spoilage	Yes	No	No	No

As nouns, spoilage is a hypernym of mildew; that is, spoilage is a word with a broader meaning than mildew:

Other hypernyms of mildew include spoiling.

mildew (noun)	spoilage (noun)
a fungus that produces a superficial (usually white) growth on organic matter	the act of spoiling something by causing damage to it
the process of becoming mildewed	the process of becoming spoiled
	the amount that has spoiled

mildew (verb)	spoilage (verb)
become moldy; spoil due to humidity