A Tank

1. A closed container for liquids or gases.
2. An open container or pool for storing water or other liquids.
3. A pond, pool, or small lake, natural or artificial.
4. The fuel reservoir of a vehicle.
5. The amount held by a container; a tankful.
6. An armoured fighting vehicle, armed with a gun in a turret, and moving on caterpillar tracks.
7. (Australian and Indian English) A reservoir or dam.
8. (Southwestern US, chiefly Texas) A large metal container for holding drinking water for animals, usually placed near a wind-driven water pump, in an animal pen or field.
9. (Southwestern US, chiefly Texas) By extension a small pond for the same purpose.
10. (slang) A very muscular and physically imposing person. Somebody who is built like a tank.
11. (role-playing games, board games, video games) a unit or character designed primarily around damage absorption and holding the attention of the enemy (as opposed to dealing damage, healing, or other tasks)
12. (US, slang) A prison cell, or prison generally.

(military fighting vehicle): battle tank, combat tank, armour (mass noun), tango (Canadian military slang)

(military fighting vehicle): armoured fighting vehicle, armored fighting vehicle, AFV, armoured combat vehicle, armored combat vehicle

(military fighting vehicle): infantry tank (historical), cavalry tank (historical), fast tank (historical), cruiser tank (historical), superheavy tank (historical), tankette (historical), bobbin tank (historical), light tank, medium tank, heavy tank, main battle tank, MBT, flail tank, flame tank, flamethrower tank

(military fighting vehicle): armoured car, armoured train, armoured personnel carrier, armored personnel carrier, APC, infantry fighting vehicle, IFV, self-propelled gun, SPG, tank destroyer, assault gun