eupneic vs breathing

eupneic is not a noun while breathing is a noun.

Word	Noun	Adjective	Verb	Adverb
eupneic	No	Yes	No	No
breathing	Yes	Yes	No	No

As adjectives, eupneic and breathing are synonyms defined as:

eupneic and breathing: passing or able to pass air in and out of the lungs normally; sometimes used in combination

Other synonyms of eupneic include eupnoeic.

eupneic (noun)	breathing (noun)
	the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation

eupneic (adjective)	breathing (adjective)
passing or able to pass air in and out of the lungs normally; sometimes used in combination	passing or able to pass air in and out of the lungs normally; sometimes used in combination