Canteen derives from the Italian cantina or wine cellar, and originally meant a place on a military establishment where soldiers could get refreshments. It continues to be used in this sense to indicate places of work where food etc. is provided from a central servery. Mobile canteens also supply troops in the field when on exercise or conducting operations. Canteen more often refers to a water bottle carried by individual soldiers as part of their personal equipment, often with a specially designed pouch or cloth cover.
— Jon Robb-Webb
n. 1. a restaurant provided by a military camp for its personnel.
2. a small water bottle, as used by soldiers or campers.
See the Introduction, Abbreviations and Pronunciation for further details.