The Collaborative International Dictionary of English v.0.48:

Tank \Tank\ (t[a^][ng]k), n.
   A small Indian dry measure, averaging 240 grains in weight;
   also, a Bombay weight of 72 grains, for pearls. --Simmonds.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Tank \Tank\ (t[a^][ng]k), n. [Pg. tanque, L. stangum a pool; or
   perhaps of East Indian origin. Cf. Stank, n.]
   1. A large basin or cistern; an artificial receptacle for
      liquids.
      [1913 Webster]

   2. A pond, pool, or small lake, natural or artificial.
      [Webster 1913 Suppl.]

            We stood in the afterglow on the bank of the tank
            and saw the ducks come home.          --F.
                                                  Remington.

            The tanks are full and the grass is high. --Lawson.
      [Webster 1913 Suppl.]

   3. (Mil.) a heavily armored combat vehicle which moves on
      caterpillar treads, rather than wheels. It typically
      carries a cannon and a heavy machine, and sometimes other
      weapons. It is the main distinguishing weapon of an
      armored division.
      [PJC]

   4. a jail cell for temporarily holding prisoners, as in a
      police station.
      [PJC]

   Tank engine, a locomotive which carries the water and fuel
      it requires, thus dispensing with a tender.

   Tank iron, plate iron thinner than boiler plate, and
      thicker than sheet iron or stovepipe iron.

   Tank worm (Zool.), a small nematoid worm found in the water
      tanks of India, supposed by some to be the young of the
      Guinea worm.
      [1913 Webster]

WordNet (r) 3.0 (2006):

tank
    n 1: an enclosed armored military vehicle; has a cannon and
         moves on caterpillar treads [syn: tank, army tank,
         armored combat vehicle, armoured combat vehicle]
    2: a large (usually metallic) vessel for holding gases or
       liquids [syn: tank, storage tank]
    3: as much as a tank will hold [syn: tank, tankful]
    4: a freight car that transports liquids or gases in bulk [syn:
       tank car, tank]
    5: a cell for violent prisoners [syn: cooler, tank]
    v 1: store in a tank by causing (something) to flow into it
    2: consume excessive amounts of alcohol
    3: treat in a tank; "tank animal refuse"

Moby Thesaurus II by Grady Ward, 1.0:

159 Moby Thesaurus words for "tank":
   Pullman, Pullman car, archives, armory, arsenal, artificial lake,
   attic, bag, baggage car, bank, barrel, basement, basket, bay,
   bayou lake, bin, bonded warehouse, bookcase, bottle, box, box up,
   boxcar, bunker, buttery, caboose, can, capsule, car, cargo dock,
   carriage, carton, case, cask, cellar, chair car, chest, cistern,
   closet, coach, coal car, conservatory, covered waggon, crate, crib,
   cupboard, dam, day coach, dead water, depository, depot, dike,
   diner, dinghy, dining car, dock, drawer, drawing room, dump,
   encase, encyst, etang, exchequer, farm pond, fishpond, flat,
   flatcar, freshwater lake, glacial lake, glory hole, godown,
   gondola, hamper, hold, hutch, inland sea, jar, lagoon, laguna,
   lake, lakelet, landlocked water, library, linn, local, loch,
   locker, lough, luggage van, lumber room, lumberyard, magasin,
   magazine, mail car, mail van, mere, millpond, millpool, nyanza,
   oxbow lake, pack, package, palace car, parcel, parlor car,
   passenger car, plash, pond, pondlet, pool, pot, puddle, rack,
   railway car, reefer, refrigerator car, repertory, repository,
   reservoir, rick, roomette, sack, salina, salt pond, shelf, sleeper,
   smoker, smoking car, stack, stack room, stagnant water,
   standing water, still water, stock room, stockcar, storage, store,
   storehouse, storeroom, sump, supply base, supply depot, tarn,
   tender, tidal pond, tin, treasure house, treasure room, treasury,
   truck, van, vat, vault, volcanic lake, waggon, warehouse,
   water hole, water pocket, well, wine cellar