room vs breathing room

room and breathing room both are nouns.

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

As nouns, breathing room is a hyponym of room; that is, breathing room is a word with a more specific, narrower meaning than room:

room (noun)	breathing room (noun)
an area within a building enclosed by walls and floor and ceiling	sufficient room for easy breathing or movement
the people who are present in a room
space for movement
opportunity for

room (verb)	breathing room (verb)
live and take one's meals at or in