electric chair

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device used in the electrocution of a person sentenced to death, consisting of a chair in which the person is restrained and a means of applying a lethal electrical current to the body.
• noun Execution by means of such a device.
• noun The sentence of death by means of such a device.

from the GNU version of the Collaborative International Dictionary of English.

• noun a device used for execution of criminals, consisting of a specially designed chair in which the victim is killed by passing a large current of electricity through the body. This method of killing is called electrocution.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A device used for performing execution by electrocution.
• noun An electrically powered wheelchair

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an instrument of execution by electrocution; resembles an ordinary seat for one person