Source : Webster's Revised Unabridged Dictionary (1913)

D'eculassement \D['e]`cu`lasse`ment"\, n. [F.] Also, sometimes,
   Anglicized Deculassment \Dec`u*lass"ment\(Ordnance)
   An accidental blowing off of, or other serious damage to, the
   breechblock of a gun; also, a removal of the breechblock for
   the purpose of disabling the gun.