The Collaborative International Dictionary of English v.0.48:

Tetrazine \Tet*raz"ine\, n. Also -in \-in\ . [Tetrazo- + -ine.]
   (Chem.)
   A hypothetical compound, C2H2N4 which may be regarded as
   benzene with four CH groups replaced by nitrogen atoms;
   also, any of various derivatives of the same. There are three
   isomeric varieties.
   [Webster 1913 Suppl.]