fall like dominoes

Domino Dom"i*no, n.; pl. {Dominos} or (esp. the pieces for a game) {Dominoes}. [F. domino, or It. domin[`o], or Sp. domin['o], fr. L. dominus master. The domino was orig. a hood worn by the canons of a cathedral. See {Don}, {Dame}.] 1. A kind of hood worn by the canons of a cathedral church; a sort of amice. --Kersey. [1913 Webster]

2. A mourning veil formerly worn by women. [1913 Webster]

3. A kind of mask; particularly, a half mask worn at masquerades, to conceal the upper part of the face. Dominos were formerly worn by ladies in traveling. [1913 Webster]

4. A costume worn as a disguise at masquerades, consisting of a robe with a hood adjustable at pleasure. [1913 Webster]

5. A person wearing a domino. [1913 Webster]

6. pl. A game played by two or more persons, with twenty-eight pieces of wood, bone, or ivory, of a flat, oblong shape, plain at the back, but on the face divided by a line in the middle, and either left blank or variously dotted after the manner of dice. The game is played by matching the spots or the blank of an unmatched half of a domino already played --Hoyle. [1913 Webster]

7. One of the pieces with which the game of dominoes is played. --Hoyle.

{fall like dominoes}. To fall sequentially, as when one object in a line, by falling against the next object, causes it in turn to fall, and that second object causes a third to fall, etc.; the process can be repeated an indefinite number of times.

Note: The phrase is derived from an entertainment using dominoes arranged in a row, each standing on edge and therefore easily knocked over; when the first is made to fall against the next, it starts a sequence which ends when all have fallen. For amusement, people have arranged such sequences involving thousands of dominoes, arrayed in fanciful patterns.