Tank

1. A large basin or cistern; an artificial receptacle for liquids.
2. A pond, pool, or small lake, natural or artificial.
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.
4. a jail cell for temporarily holding prisoners, as in a police station.
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 (Zoöl.),
a small nematoid worm found in the water tanks of India, supposed by some to be the young of the Guinea worm.