To play dummy

Dummy Dum"my, n.; pl. {Dummies}. 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.