The Collaborative International Dictionary of English v.0.48:

Detonator \Det"o*na`tor\ (d[e^]t"[-o]*n[=a]`t[~e]r), n.
   One that detonates; specif.:
   (a) An explosive whose action is practically instantaneous.
   (b) Something used to detonate a charge, as a detonating
       fuse.
   (c) A case containing detonating powder, the explosion of
       which serves as a signal, as on railroads.
   (d) A gun fired by a percussion cap. [Obs.]
       [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

detonator
    n 1: a mechanical or electrical explosive device or a small
         amount of explosive; can be used to initiate the reaction
         of a disrupting explosive [syn: detonator, detonating
         device, cap]