What does "dummy" mean?

Additional senses

1. 2.One who is dumb. H. Smith.
2. 3.A sham package in a shop, or one which does not contain what its exterior indicates.
3. 4.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. 5.(Drama) One who plays a merely nominal part in any action; a sham character.
5. 6.A thick-witted person; a dolt. [Colloq.]
6. 7.(Railroad) A locomotive with condensing engines, and, hence, without the noise of escaping steam; also, a dummy car.
7. 8.(Card Playing) The fourth or exposed hand when three persons play at a four- handed game of cards.
8. 9.A floating barge connected with a pier. Knight. To play dummy, to play the exposed or dummy hand in cards. The partner of the dummy plays it.