The Collaborative International Dictionary of English v.0.48:

Cacodyl \Cac"o*dyl\, n. [Gr. ??????? ill-smelling (kako`s bad +
   ????? to smell) + -yl.] (Chem.)
   Alkarsin; a colorless, poisonous, arsenical liquid,
   As2(CH3)4, spontaneously inflammable and possessing an
   intensely disagreeable odor. It is the type of a series of
   compounds analogous to the nitrogen compounds called
   hydrazines. [Written also cacodyle, and kakodyl.]
   [1913 Webster]