WordNet (r) 3.0 (2006):

gas chamber
    n 1: instrument of execution consisting of a sealed chamber into
         which poison gas is introduced; used to kill people or
         animals [syn: gas chamber, death chamber]

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "gas chamber":
   Belsen, abattoir, aceldama, ax, beheading, block, burning,
   butchery, capital punishment, concentration camp, cross,
   crucifixion, death chair, death chamber, decapitation, decollation,
   defenestration, drop, electric chair, electrocution, execution,
   field of blood, fusillade, gallows, gallows-tree, garrote, gassing,
   gibbet, guillotine, halter, hanging, hemlock, hemp, hempen collar,
   hot seat, judicial murder, lapidation, lethal chamber, maiden,
   necktie party, noose, poisoning, rope, scaffold, shambles,
   shooting, slaughterhouse, stake, stockyard, stoning, strangling,
   strangulation, the ax, the block, the chair, the gallows,
   the gas chamber, the guillotine, the hot seat, the rope, tree