N insensibility, physical insensibility, obtuseness, palsy, paralysis, paraesthesia, anaesthesia, sleep, hemiplegia, motor paralysis, vegetable state, coma, anaesthetic agent, opium, ether, chloroform, chloral, nitrous oxide, laughing gas, exhilarating gas, protoxide of nitrogen, refrigeration, insensible, unfeeling, senseless, impercipient, callous, thick- skinned, pachydermatous, hard, hardened, case hardened, proof, obtuse, dull, anaesthetic, comatose, paralytic, palsied, numb, dead.

For further exploring for "nitrous oxide" in Webster Dictionary Online