breathlessness vs shortness of breath

breathlessness and shortness of breath both are nouns.

Word	Noun	Adjective	Verb	Adverb
breathlessness	Yes	No	No	No
shortness of breath	Yes	No	No	No

As nouns, breathlessness and shortness of breath are synonyms defined as:

Other synonyms of breathlessness include SOB.

breathlessness (noun)	shortness of breath (noun)
a dyspneic condition	a dyspneic condition