1 An instrument that measures and gives a visual display of the amount, level, or contents of something.
1.1 A tool for checking whether something conforms to a desired dimension.
1.2 A means of estimating something.
2 The thickness, size, or capacity of something, especially as a standard measure.
2.1 The diameter of a wire, fibre, tube, etc.
2.2 in combination A measure of the diameter of a gun barrel, or of its ammunition, expressed as the number of spherical pieces of shot of the same diameter as the barrel that can be made from 1 lb (454 g) of lead.
as modifier ‘a 12-gauge shotgun’
2.3 in combination The thickness of sheet metal or plastic. – as modifier ‘500-gauge polythene’
2.4 The distance between the rails of a line of railway track.
3 Nautical – archaic The position of a sailing ship to windward (the weather gage) or leeward (the lee gage) of another.
Middle English (denoting a standard measure): from Old French gauge (noun), gauger (verb), variant of Old Northern French jauge (noun), jauger (verb), of unknown origin.
This 3D-printed track set has a gauge of 36mm between the rails.
[[It was only after an early morning appointment that I gauged the amount of time still left before the day got away from me, so I quickly checked to see if this word was available. Luck was with me, and I had an illustrative image ready to go.]]