an instrument for measuring or testing something, e.g. a dimension or quantity

a measure of the size of the bore of a shotgun

the distance between the rails of a railway, wheels on an axle, etc

archaic the relative position of a ship with reference to another ship and the wind

to measure exactly the size, dimensions, capacity, or contents of (something)

to estimate or judge (something)

Can you gauge his reaction?

to check (something) for conformity to specifications or limits