The Collaborative International Dictionary of English v.0.48:

Canteen \Can*teen"\ (k[a^]n*t[=e]n"), n. [F. cantine bottle
   case, canteen (cf. Sp. & It. cantina cellar, bottle case),
   either contr. fr. It. canovettina, dim. of canova cellar, or,
   more likely, fr. OF. cant. corner, It. & Sp. canto. See 1st
   Cant.] (Mil.)
   1. A small vessel used by soldiers or hikers for carrying
      water, liquor, or other drink. [Written also cantine.]
      [1913 Webster]

   Note: In 1910 in the English service the canteen is made of
         wood and holds three pints; in the United States it is
         usually a tin flask.
         [1913 Webster]

   2. A chest containing culinary and other vessels for military
      officers in a garrison.
      [1913 Webster]

   3. The sutler's shop in a garrison.
      [1913 Webster]

   4. Hence: A store or small shop within a larger establishment
      where refreshments and sometimes other supplies are sold.
      At a military base the canteen may be as large as a
      general store; within a school or small company it may be
      only a small counter with very limited supplies, or a
      snack bar.
      [PJC]

   5. A temporary location where food is dispensed during an
      emergency.
      [PJC]

WordNet (r) 3.0 (2006):

canteen
    n 1: a flask for carrying water; used by soldiers or travelers
    2: sells food and personal items to personnel at an institution
       or school or camp etc.
    3: a restaurant outside; often for soldiers or policemen [syn:
       canteen, mobile canteen]
    4: a recreation room in an institution
    5: restaurant in a factory; where workers can eat

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "canteen":
   PX, automat, beanery, bistro, buffet, buvette, cafe, cafeteria,
   calabash, cantina, carafe, carboy, caster, chophouse, chuck wagon,
   coffee shop, coffeehouse, coffeeroom, commissary, cookhouse,
   cookshack, cookshop, cruet, cruse, decanter, demijohn, diner,
   dining hall, dining room, dog wagon, drive-in, drive-in restaurant,
   eatery, eating house, ewer, fast-food chain, fifth, flacon, flagon,
   flask, flasket, gourd, grill, grillroom, hamburger stand,
   hash house, hashery, hipflask, hot-dog stand, hot-water bottle,
   jar, jeroboam, jug, kitchen, lota, lunch counter, lunch wagon,
   luncheonette, lunchroom, magnum, mess hall, mussuk, olla, phial,
   pizzeria, post exchange, quick-lunch counter, restaurant,
   smorgasbord, snack bar, stoup, tavern, tearoom, trattoria