poison gas a gas that is poisonous to breath or contact; used in chemical warfare
agent an active and efficient cause; capable of producing a certain effect; "their research uncovered new disease agents"
vx gas a highly lethal nerve agent used in chemical warfare; a toxic liquid that penetrates the skin or lungs to disrupt the nervous system and stop respiration; in combat VX gas is deployed by detonating a container over the target area and can persist in the environment up to several weeks after release; "VX gas is one of those things we wish we could disinvent"