trick [LME] A medieval word from Old French trichier ‘to deceive or cheat’, which also gave us treachery [ME]. A 16th-century sense of the word was ‘habit’, which is where the expression up to your old tricks comes from. Children say trick or treat at Halloween when they call at houses, threatening to play a trick on the householder unless a treat is produced in the form of sweets or money. The phrase did not appear until the 1930s in the USA.