Cacodyl

from WordNet (r) 3.0 (2006)

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

from 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]