breather vs rest period

breather and rest period both are nouns.

Word	Noun	Adjective	Verb	Adverb
breather	Yes	No	No	No
rest period	Yes	No	No	No

As nouns, rest period is a hypernym of breather; that is, rest period is a word with a broader meaning than breather:

Other hypernyms of breather include relief, respite, rest.

breather (noun)	rest period (noun)
air passage provided by a retractable device containing intake and exhaust pipes; permits a submarine to stay submerged for extended periods of time	a pause for relaxation
a short respite