room vs headroom

room and headroom both are nouns.

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

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

room (noun)	headroom (noun)
an area within a building enclosed by walls and floor and ceiling	the capacity of a system to reproduce loud sounds without distortion
the people who are present in a room	vertical space available to allow easy passage under something
space for movement
opportunity for

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