hen's tooth

plural hen's teeth · plural hens' teeth

1. idiomaticAnything not naturally occurring.

   as rare as a hen's tooth

   1 more example

   Indeed, many of the Dutch in Pernambuco were won over to the Church of Rome, ‘whereas converts from Catholicism to Calvinism were as rare as hens’ teeth’.

   1992, Edwin Williamson, The Penguin history of Latin America, London; New York: Penguin Books, →ISBN, page 183

   Synonyms: rocking horse shit, black swan, lightning in a bottle, one in a million, rara avis, rare bird, rarity, rocking horse shit