domino (n.)

1801, "one of the pieces with which the game of dominoes is played," from French domino (1771), perhaps (on a perceived resemblance to the black tiles of the game) from the earlier meaning "hood with a cloak worn by canons or priests over other vestments in cold weather" (1690s in English), from Latin dominus "lord, master" (from domus "house," from PIE root *dem- "house, household"), but the connection is not clear.

Metaphoric use in geopolitics dates to 1953, when U.S. President Eisenhower used the image in reference to what happens when you set dominoes upright in a row and knock the first one down. It came to be known as the domino theory.

President Eisenhower, on August 4, 1953, explained that if Indonesia fell, "the peninsula, the last little bit of land hanging on down there, would be scarcely defensible." "All India," he continued, "would be outflanked," and "Burma would be in no position for defense. On April 7, 1954, the President was still warning that if Indochina fell, all of southeast Asia would collapse like "falling dominoes." The President said, that as the last domino in the line falls inevitably from the toppling of the first, the loss of Indochina would lead to the loss of Burma, of Thailand, and Indonesia, and a threat to Australia and New Zealand. [Rep. Joseph R. McCarthy, Congressional Record, Aug. 2, 1955]