rarity, rareness, infrequency (noun)

noteworthy scarcity

rarity, tenuity, low density (noun)

a rarified quality

"the tenuity of the upper atmosphere"

curio, curiosity, oddity, oddment, peculiarity, rarity (noun)

something unusual -- perhaps worthy of collecting

rarity (Noun)

A rare object.

rarity (Noun)

A measure of the scarcity of an object.

rarity (Noun)

Thinness; the property of having low density