respiratory illness vs respiratory disease

respiratory illness and respiratory disease both are nouns.

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

As nouns, respiratory illness and respiratory disease are synonyms defined as:

respiratory illness and respiratory disease: a disease affecting the respiratory system

Other synonyms of respiratory illness include respiratory disorder.

respiratory illness (noun)	respiratory disease (noun)
a disease affecting the respiratory system	a disease affecting the respiratory system