The Collaborative International Dictionary of English v.0.48:

Tetryl \Tet"ryl\, n. [Tetra- + -yl.] (Chem.)
   Butyl; -- so called from the four carbon atoms in the
   molecule.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tetryl
    n 1: a yellow crystalline explosive solid that is used in
         detonators [syn: tetryl, nitramine]