aqualung vs breathing device

aqualung and breathing device both are nouns.

Word	Noun	Adjective	Verb	Adverb
aqualung	Yes	No	No	No
breathing device	Yes	No	No	No

As nouns, breathing device is a hypernym of aqualung; that is, breathing device is a word with a broader meaning than aqualung:

aqualung: a device (trade name Aqua-Lung) that lets divers breathe under water; scuba is an acronym for self-contained underwater breathing apparatus
breathing device: a device that facilitates breathing in cases of respiratory failure

Other hypernyms of aqualung include breathing apparatus, breathing machine, ventilator.

aqualung (noun)	breathing device (noun)
a device (trade name Aqua-Lung) that lets divers breathe under water; scuba is an acronym for self-contained underwater breathing apparatus	a device that facilitates breathing in cases of respiratory failure