noun 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.
noun A container used to discreetly carry a small amount of a hard alcoholic beverage; a pocket flask.
noun 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.
noun A container for holding a casting mold, especially for sand casting molds.
noun A bed in a gun carriage.
(The addition of quotations indicative of this usage is being sought:)
noun A nuclear flask, a large, secure lead-lined container for the transport of nuclear material.
noun A small bottle of liquor.
verb To invest a denture in a flask so as to produce a sectional mold.