a measuring instrument for measuring and indicating a quantity such as the thickness of wire or the amount of rain etc.

accepted or approved instance or example of a quantity or quality against which others are judged or measured or compared

the distance between the rails of a railway or between the wheels of a train

the thickness of wire

diameter of a tube or gun barrel

judge tentatively or form an estimate of (quantities or time)

rub to a uniform size

determine the capacity, volume, or contents of by measurement and calculation

measure precisely and against a standard

adapt to a specified measurement

mix in specific proportions

a particle that mediates the interaction of two elementary particles