rarity vs physical object

rarity and physical object both are nouns.

Word	Noun	Adjective	Verb	Adverb
rarity	Yes	No	No	No
physical object	Yes	No	No	No

As nouns, physical object is a hypernym of rarity; that is, physical object is a word with a broader meaning than rarity:

rarity: something unusual -- perhaps worthy of collecting
physical object: a tangible and visible entity; an entity that can cast a shadow

Other hypernyms of rarity include object.

rarity (noun)	physical object (noun)
something unusual -- perhaps worthy of collecting	a tangible and visible entity; an entity that can cast a shadow
a rarified quality
noteworthy scarcity