respiratory illness vs disease

respiratory illness and disease both are nouns.

Word	Noun	Adjective	Verb	Adverb
respiratory illness	Yes	No	No	No
disease	Yes	No	No	No

As nouns, disease is a hypernym of respiratory illness; that is, disease is a word with a broader meaning than respiratory illness:

respiratory illness (noun)	disease (noun)
a disease affecting the respiratory system	an impairment of health or a condition of abnormal functioning