1) Aonemillion 1) Absence of solidity 2) Blue moon 3) Canadian pop punk group 4) Compressibility 5) Curiosity 6) Diamond value factor 7) Fictional unicorn 8) French word used in English 9) Highly unusual occurrence 10) Infrequency 11) Infrequently seen thing 12) It hardly ever happens 13) It occurs once in a blue moon 1) Curio 2) Fewness 3) Infrequency 4) Knickknackery 5) Nicknack 6) Rareness 7) Scarcity 8) Showpiece 9) Unconformity 10) Whatnot 
Rarity can refer to: People, including: Fictional characters, including: ...
• (n.) The quality or state of being rare; rareness; thinness; as, the rarity (contrasted with the density) of gases. • (n.) That which is rare; an uncommon thing; a thing valued for its scarcity.
Generally relates to the infrequency or relative unavailability of a coin, as a direct function of important factors such as the original mintage and overall survival rate.
Rar'i·ty (răr'ĭ*tȳ; 277) noun ; plural Rarities (- tĭz). [ Latin raritas : confer French rareté . See Rare .] 1. The quality or state of being rare; rareness; thinness; as, the rarity (contrasted with the density ) ...
[n] - noteworthy scarcity 2. [n] - a rarified quality
infrequency noun noteworthy scarcity