The Oxford Thesaurus An A-Z Dictionary of Synonyms - rarityn.

1) curiosity, oddity, curio, collector's item, find, treasure, conversation piece, Brit one-off, Colloq Brit oner: Among the rarities in his collection is a stuffed dodo. 2) unusualness, uncommonness, rareness, uniqueness, scarcity: The rarity of the first edition makes this book all the more valuable.