to play dummy

Webster's Dictionary (GCIDE)

1.One who is dumb. --H. Smith. [1913 Webster]

2.A sham package in a shop, or one which does not contain what its exterior indicates. [1913 Webster]

3.An imitation or copy of something, to be used as a substitute; a model; a lay figure; as, a figure on which clothing is exhibited in shop windows; a blank paper copy used to show the size of the future book, etc. [1913 Webster]

4.(Drama) One who plays a merely nominal part in any action; a sham character. [1913 Webster]

5.A thick-witted person; a dolt. [Colloq.] [1913 Webster]

6.(Railroad) A locomotive with condensing engines, and, hence, without the noise of escaping steam; also, a dummy car. [1913 Webster]

7.(Card Playing) The fourth or exposed hand when three persons play at a four-handed game of cards. [1913 Webster]

8.A floating barge connected with a pier. --Knight. [1913 Webster]

To play dummy, to play the exposed or dummy hand in cards. The partner of the dummy plays it. Dumose