From Longman Dictionary of Contemporary Englishbe a raritybe a rarityRAREto not happen or exist very often Visitors were a rarity in the village. → rarity
Examples from the Corpus
be a rarity• A sheriff who is dumb is a rarity.• Breadwinner wives who are the couple's sole earners are a rarity, wives are typically joint but secondary earners.• A member of the flock was a rarity, but which was it?• In short, while most judiciaries exercise some discretion in adjudication, the existence of a truly independent judiciary is a rarity.• Unlike the West, business luncheons are a rarity and evening entertainment almost never takes place in the home.• The campaigners Margaret Thatcher is a rarity among national leaders in that she has a science background.• I decided to skip dessert, which is a rarity for me. 