cistern vs flask

cistern

noun
  • In a flush toilet, the container in which the water used for flushing is held; a toilet tank. 

  • The vessel surrounding the condenser in a steam engine. 

  • A cisterna. 

  • A reservoir or tank for holding water, especially for catching and holding rainwater for later use. 

flask

noun
  • A container used to discreetly carry a small amount of a hard alcoholic beverage; a pocket flask. 

  • Laboratory glassware used to hold larger volumes than test tubes, normally having a narrow mouth of a standard size which widens to a flat or spherical base. 

  • A container for holding a casting mold, especially for sand casting molds. 

  • A narrow-necked vessel of metal or glass, used for various purposes; as of sheet metal, to carry gunpowder in; or of wrought iron, to contain quicksilver; or of glass, to heat water in, etc. 

  • A bed in a gun carriage. 

verb
  • To invest a denture in a flask so as to produce a sectional mold. 

How often have the words cistern and flask occurred in a corpus of books? (source: Google Ngram Viewer )