The Collaborative International Dictionary of English v.0.48:

fulminate of mercury \ful"mi*nate of mer"cu*ry\, n. (Chem.)
   The mercury salt of fulminic acid (Hg(CNO)2), called also
   mercury fulminate. It is prepared as gray crystals, and is
   used primarily in detonators for detonating high explosives,
   such as dynamite or TNT.
   [PJC]

The Collaborative International Dictionary of English v.0.48:

mercury fulminate \mer"cu*ry ful"mi*nate\, n. (Chem.)
   The mercury salt of fulminic acid (Hg(CNO)2), called also
   fulminate of mercury. It is an explosive compound prepared
   as gray crystals, and is used primarily in detonators for
   detonating high explosives, such as dynamite or TNT. It is
   sensitive to shock and may be detonated by a blow.
   [PJC]

WordNet (r) 3.0 (2006):

fulminate of mercury
    n 1: a fulminate that when dry explodes violently if struck or
         heated; used in detonators and blasting caps and percussion
         caps [syn: mercury fulminate, fulminate of mercury,
         fulminating mercury]