rarity (n.)youdaoicibaDictYouDict[rarity 词源字典]
early 15c., "thinness;" 1550s, "fewness," from Middle French rarité or directly from Latin raritas "thinness, looseness of texture; fewness," from rarus (see rare (adj.1)). Sense of "a rare thing or event" is from 1590s.[rarity etymology, rarity origin, 英语词源]