A poison gas used in World War I; it is also slightly lacrimatoric.
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di·phos·gene (')dī-'fäz-.jēn n a liquid compound C2Cl4O2 used as a poison gas in World War I
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di·phos·gene (di-fosґjēn) a gas which is intensely irritating to the lungs, producing pulmonary edema.Medical dictionary. 2011.