Source : Webster's Revised Unabridged Dictionary (1913)

Cacodyl \Cac"o*dyl\, n. [Gr. ??????? ill-smelling (????? 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}.]

Source : WordNet®

cacodyl
     n 1: a poisonous oily liquid with a garlicky odor composed of 2
          cacodyl groups; undergoes spontaneous combustion in dry
          air [syn: {tetramethyldiarsine}]
     2: the univalent group derived from arsine [syn: {cacodyl group},
         {cacodyl radical}, {arsenic group}]