breathing vs eupneic

breathing is a noun but eupneic is not a noun.

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

As adjectives, breathing and eupneic are synonyms defined as:

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

Other synonyms of breathing include eupnoeic.

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

breathing (adjective)	eupneic (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