ill health vs malady

ill health and malady both are nouns.

Word	Noun	Adjective	Verb	Adverb
ill health	Yes	No	No	No
malady	Yes	No	No	No

As nouns, malady is a hyponym of ill health; that is, malady is a word with a more specific, narrower meaning than ill health:

ill health: a state in which you are unable to function normally and without pain
malady: impairment of normal physiological function affecting part or all of an organism

ill health (noun)	malady (noun)
a state in which you are unable to function normally and without pain	impairment of normal physiological function affecting part or all of an organism
	any unwholesome or desperate condition