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]

Moby Thesaurus II by Grady Ward, 1.0:

53 Moby Thesaurus words for "dining room":
   automat, beanery, bistro, buffet, buvette, cafe, cafeteria,
   canteen, cantina, chophouse, chuck wagon, coffee shop, coffeehouse,
   coffeeroom, commons, cookhouse, cookshack, cookshop, diner,
   dinette, dining car, dining hall, dining saloon, dog wagon,
   drive-in, drive-in restaurant, eatery, eating house,
   fast-food chain, grill, grillroom, hamburger stand, hash house,
   hashery, hot-dog stand, kitchen, lunch counter, lunch wagon,
   luncheonette, lunchroom, mess, mess hall, messroom, pizzeria,
   quick-lunch counter, refectory, restaurant, salle a manger,
   smorgasbord, snack bar, tavern, tearoom, trattoria