Pronunciation: (râr'i-tē),[key] —n., —pl.-ties. 1. something rare, unusual, or uncommon: Snowstorms are a rarity in the South. 2. something esteemed or interesting in being rare, uncommon, or curious: That folio is a rarity that will bring a good price. 3. the state or quality of being rare.
4. rare occurrence; infrequency: Volcanic eruptions on the island occur with great rarity. 5. unusual excellence.
6. thinness, as of air or a gas.