What is "tank worm"

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.

2. A pond, pool, or small lake, natural or artificial.

   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.

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 (Zo["o]l.), a small nematoid worm found in the water tanks of India, supposed by some to be the young of the Guinea worm.