poison gas

any of various toxic gases, especially those used in chemical warfare to kill or incapacitate on inhalation or contact, as phosgene, chlorine, etc.

Origin of poison gas

First recorded in 1910–15

To begin with, he did not believe in them; they were just a part of the poison-gas of war.

Jimmie Higgins |Upton Sinclair
Acid sprays and poison-gas of various kinds had been tried without appreciable effect.

Astounding Stories, August, 1931 |Various
There was poison-gas and smoke-gas, terrible artillery, awful rifle-fire, and of course the rifle and bayonet.

In the Line of Battle |Various
I have said that it was about four oclock in the afternoon when we had our first experience of the poison-gas.

In the Line of Battle |Various

Just wait for the results of the poison-gas competition presumably.

Fantasia of the Unconscious |D. H. Lawrence

poison gas

a gaseous substance, such as chlorine, phosgene, or lewisite, used in warfare to kill or harm

poison gas

A gas or vapor used especially in chemical warfare to injure, disable, or kill upon inhalation or contact.