Ethyldichloroarsine, also known as ED, CY, and ethyl Dick, is an organoarsenic compound with the formula CH₃CH₂AsCl₂. This colourless volatile liquid is a highly toxic vesicant (blister agent) that was used during World War I in chemical warfare. The molecule is pyramidal with the Cl–As–Cl and C–As–Cl angles approaching 90° (see image). Ethyldichloroarsine has high chronic toxicity, similar to lewisite.