a graduated instrument or vessel for gauging or measuring the force or quantity of a fluctuating object, as a rainfall, tide, stream, wind, etc., a contrivance attached to a vessel, esp. a boiler, to show the height or condition of its contents; more fully gauge-cock, -glass. Of an air-pump: An instrument which points out the degree of exhaustion in the receiver; usually with word prefixed specifying the form of gauge, as barometer, siphon gauge., an object or instrument for the measurement of dimensions, pressure, volume etc.