The Collaborative International Dictionary of English v.0.48:

Tetrazole \Tet*raz"ole\, n. [Tetrazo- + -ole.] (Org. Chem.)
   A crystalline acid substance, CH2N4, which may be regarded
   as pyrrol in which nitrogen atoms replace three CH groups;
   also, any of various derivatives of the same.
   [Webster 1913 Suppl.]