Definition of "cistern"

cistern

/ˈsɪs.tən/

noun
plural cisterns
1. A reservoir or tank for holding water, especially for catching and holding rainwater for later use.
  Quotations
  Their extreme necessity is attested by the countless number of old, unused cisterns with which the Holy Land is literally honeycombed.
  1913, A.C. Cotter, Catholic Encyclopedia, "Wells in Scripture"
  Cisterns (bôr, bō'r), mentioned frequently in the Bible, are artificial reservoirs, usually cut into bedrock, for collecting and conserving rain runoff from roofs and courtyards.
  2001, Philip J. King, Lawrence E. Stager, chapter 3, in Life in Biblical Israel, page 126
2. In a flush toilet, the container in which the water used for flushing is held; a toilet tank.
  Quotations
  It is possible to connect your tank to your toilet cistern and/or garden, so that even if the water is not drinkable it still can be used productively to make major water savings.
  2003, Allan Windust, chapter 9, in Waterwise House & Garden: a Guide for Sustainable Living, page 36
3. A cisterna.
4. The vessel surrounding the condenser in a steam engine.