roominess vs bigness

roominess and bigness both are nouns.

Word	Noun	Adjective	Verb	Adverb
roominess	Yes	No	No	No
bigness	Yes	No	No	No

As nouns, bigness is a hypernym of roominess; that is, bigness is a word with a broader meaning than roominess:

roominess: spatial largeness and extensiveness (especially inside a building)
bigness: the property of having a relatively great size

Other hypernyms of roominess include largeness.

roominess (noun)	bigness (noun)
spatial largeness and extensiveness (especially inside a building)	the property of having a relatively great size
intellectual breadth