eupnoea vs external respiration

eupnoea and external respiration both are nouns.

Word	Noun	Adjective	Verb	Adverb
eupnoea	Yes	No	No	No
external respiration	Yes	No	No	No

As nouns, external respiration is a hypernym of eupnoea; that is, external respiration is a word with a broader meaning than eupnoea:

eupnoea: normal relaxed breathing
external respiration: the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation

Other hypernyms of eupnoea include breathing, respiration, ventilation.

eupnoea (noun)	external respiration (noun)
normal relaxed breathing	the bodily process of inhalation and exhalation; the process of taking in oxygen from inhaled air and releasing carbon dioxide by exhalation