dummy (n.)

1590s, "mute person," from dumb (adj.) + -y (3). Extended by 1845 to "figure representing a person," hence "counterfeit object, something that imitates a reality for mechanical purposes." In card games (originally whist, later bridge) "exposed hand of cards placed face-up," by 1736. Meaning "dolt, blockhead" is from 1796.

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Definitions of dummy from WordNet
dummy (n.)
a person who does not talk;
Synonyms: silent person
dummy (n.)
an ignorant or foolish person;
Synonyms: dumbbell / dope / boob / booby / pinhead
dummy (n.)
a figure representing the human form;
dummy (n.)
a cartridge containing an explosive charge but no bullet;
Synonyms: blank / blank shell
dummy (v.)
make a dummy of;
dummy up the books that are to be published
Synonyms: dummy up
dummy (adj.)
having the appearance of being real but lacking capacity to function;
a dummy corporation