Is it ensure, insure, or assure?
HORSE-SHOES, the game of coits, or quoits--because sometimes actually played with horse-shoes. [John Trotter Brockett, "A Glossary of North Country Words," 1829]The belief that finding a horseshoe by chance is lucky is attested from late 14c., and the practice of nailing one above a doorway to prevent a witch entering therein was common in London down to c.1800. Of a type of bend in a river, 1770, American English. As a type of crab, from 1775.
U-shaped metal plate by which horses' hooves are protected from wear on hard or rough surfaces. Horseshoes apparently are a Roman invention; a mule's loss of its shoe is mentioned by the Roman poet Catullus in the 1st century BC.