scuba vs breathing apparatus

scuba and breathing apparatus both are nouns.

Word	Noun	Adjective	Verb	Adverb
scuba	Yes	No	No	No
breathing apparatus	Yes	No	No	No

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

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

Other hypernyms of scuba include breathing device, breathing machine, ventilator.

scuba (noun)	breathing apparatus (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