collectable vs rarity

collectable and rarity both are nouns.

Word	Noun	Adjective	Verb	Adverb
collectable	Yes	Yes	No	No
rarity	Yes	No	No	No

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

collectable: things considered to be worth collecting (not necessarily valuable or antique)
rarity: something unusual -- perhaps worthy of collecting

Other hypernyms of collectable include curio, curiosity, oddity, oddment, peculiarity.

collectable (noun)	rarity (noun)
things considered to be worth collecting (not necessarily valuable or antique)	something unusual -- perhaps worthy of collecting
	a rarified quality
	noteworthy scarcity

collectable (adjective)	rarity (adjective)
subject to or requiring payment especially as specified