respiratory disease vs respiratory illness

respiratory disease and respiratory illness both are nouns.

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

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

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

Other synonyms of respiratory disease include respiratory disorder.

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