Source : WordNet®

VX gas
     n : 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"