The Collaborative International Dictionary of English v.0.48:

diningroom \diningroom\, dining room \dining room\n.
   a room used for dining. In a residence, it usually contains a
   dining table and some furniture, such as a buffet or
   sideboard, for storing tableware and dining utensils.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

dining-room
    n 1: a room used for dining [syn: dining room, dining-room]