dumm

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. An ignorant or thick-witted person; a foolish person; a dolt.
Syn. -- dope, boob, booby, pinhead, dumbbell. [ 1913 Webster + WordNet 1.5 ]

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.