collector's item vs oddity

collector's item and oddity both are nouns.

Word	Noun	Adjective	Verb	Adverb
collector's item	Yes	No	No	No
oddity	Yes	No	No	No

As nouns, oddity is a hypernym of collector's item; that is, oddity is a word with a broader meaning than collector's item:

collector's item: the outstanding item (the prize piece or main exhibit) in a collection
oddity: something unusual -- perhaps worthy of collecting

Other hypernyms of collector's item include curio, curiosity, oddment, peculiarity, rarity.

collector's item (noun)	oddity (noun)
the outstanding item (the prize piece or main exhibit) in a collection	something unusual -- perhaps worthy of collecting
	a strange attitude or habit
	eccentricity that is not easily explained