domino [L17th] In 16th-century French domino referred to a kind of winter cloak worn by priests. This word was used in Spain and Venice for a cloak and mask worn at masquerades, the sense first used in English. No one knows why the term was transferred to the game of dominoes at the start of the 19th century. From the 1950s the term domino theory appeared, based on the idea that events in one country will have a knock-on effect in others. It was particularly well used during the Vietnam War for the risk of surrounding countries becoming communist. This was based on the other use of dominoes, setting them on end in rows and watching the cascade of falling dominoes.