Dummy

1. One who is dumb.
2. A sham package in a shop, or one which does not contain what its exterior indicates.
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.
4. (Drama) One who plays a merely nominal part in any action; a sham character.
5. A thick-witted person; a dolt.
6. (Railroad) A locomotive with condensing engines, and, hence, without the noise of escaping steam; also, a dummy car.
7. (Card Playing) The fourth or exposed hand when three persons play at a four-handed game of cards.
8. A floating barge connected with a pier.
To play dummy ,
to play the exposed or dummy hand in cards. The partner of the dummy plays it.