The Collaborative International Dictionary of English v.0.48:

electric chair \e*lec"tric chair`\, n.
   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.

   Syn: the chair, death chair, hot seat. [PJC] electric charge

WordNet (r) 3.0 (2006):

electric chair
    n 1: an instrument of execution by electrocution; resembles an
         ordinary seat for one person; "the murderer was sentenced
         to die in the chair" [syn: electric chair, chair,
         death chair, hot seat]

Moby Thesaurus II by Grady Ward, 1.0:

23 Moby Thesaurus words for "electric chair":
   ax, block, cross, death chair, death chamber, drop, gallows,
   gallows-tree, gas chamber, gibbet, guillotine, halter, hemp,
   hempen collar, hot seat, lethal chamber, maiden, noose, rope,
   scaffold, stake, the chair, tree