cistern

Short definition from Wiktionary

Noun

1. 1
   A reservoir or tank for holding water, especially for catching and holding rainwater for later use.
2. 2
   In a flush toilet, the container in which the water used for flushing is held; a toilet tank.
3. 3
   A shallow, typically oval, vessel made of porcelain, pottery, or glass.
4. 4
   The receptacle that holds the fuel in an oil lamp.
5. 5
   A cisterna.
6. 6
   The vessel surrounding the condenser in a steam engine.