The Collaborative International Dictionary of English v.0.48:

Enlarger \En*lar"ger\, n.
   1. One who or that which enlarges.
      [1913 Webster]

   2. (Photography) an optical device for making copies of
      photographs larger than the original, having a head for
      holding the original, a source of illumination to project
      the image, and a bed for holding the sensitized
      photographic paper which will received the larger image.
      [PJC]

WordNet (r) 3.0 (2006):

enlarger
    n 1: photographic equipment consisting of an optical projector
         used to enlarge a photograph