2-氯乙烯基二氯胂(2-Chloroethenyldichloroarsine)，又名路易氏剂(Lewisite),由美国化学家W.L.Lewis(Winford Lee Lewis)于1918年春发明，是一种具有强烈皮肤糜烂毒性的有机砷化合物，在毒剂发展史上有着极其重要的地位。工业品中含有α、β、γ三种类型的路易氏剂，其中α型糜烂毒性最强，β型次之，γ型无实际军用价值。一般而言，合格的路易氏剂中主要组分为α成分，含少量β成分，不应有γ成分。β型路易氏剂通常被视为一种刺激性毒剂。

Lewisite (L) is an organoarsenic compound. It was once manufactured in the U.S., Japan, and Germany for use as a chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although colorless and odorless, impure samples of lewisite are a yellow, brown, violet-black, green, or amber oily liquid with a distinctive odor that has been described as similar to geraniums.