The Collaborative International Dictionary of English v.0.48:

flashgun \flash"gun`\ n.
   a lamp for providing intense momentary light to take a
   photograph.

   Syn: flash, photoflash, flash lamp, flashbulb.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

flashgun
    n 1: a lamp for providing momentary light to take a photograph
         [syn: flash, photoflash, flash lamp, flashgun,
         flashbulb, flash bulb]