The Collaborative International Dictionary of English v.0.48:

disc jockey \disc" jock`ey\ (d[i^]sk" j[o^]k`[y^]), n.
   a person who plays records or compact disks of recorded
   music; especially, a person who selects and plays recorded
   music for broadcast over the radio, often making comments
   about the music or other topics and also announcing
   commercial advertising messages; also, one who plays recorded
   music at a dance or social gathering, especially as a
   profession. [Also spelled disk jockey.]

   Syn: DJ. [PJC]

WordNet (r) 3.0 (2006):

disc jockey
    n 1: a person who announces and plays popular recorded music
         [syn: disk jockey, disc jockey, dj]