cistern

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

Plural cisterns