Conkers

Originally, an Anglo-Irish children's game, which the OED describes as “originally played with snail-shells, now with horse-chestnuts through which a string is threaded, the object being to break that held by the opponent.” It is first mentioned in 1821 in Robert Southey's memoirs, but the game only became popular from the 1850s. The origin of the name is uncertain. The OED says the word derives "presumably from 'conch' meaning a shell, or an association with the word 'conquer' as in winning the game". Other sources claim it was a dialect word meaning to 'knock out'. The association with the word 'conquer' seems to cover all bets, but the origin still remains obscure.