ill health vs pathology

ill health and pathology both are nouns.

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

As nouns, pathology is a hyponym of ill health; that is, pathology 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
pathology: any deviation from a healthy or normal condition

ill health (noun)	pathology (noun)
a state in which you are unable to function normally and without pain	the branch of medical science that studies the causes and nature and effects of diseases
	any deviation from a healthy or normal condition