length vs gauge

length and gauge both are nouns.

Word	Noun	Adjective	Verb	Adverb
length	Yes	No	No	No
gauge	Yes	No	Yes	No

As nouns, gauge is a hyponym of length; that is, gauge is a word with a more specific, narrower meaning than length:

length: size of the gap between two places
gauge: the distance between the rails of a railway or between the wheels of a train

Other hyponyms of length include leg, arm's length, light time, skip distance, wingspan, wingspread, wingspread, altitude.

length (noun)	gauge (noun)
a section of something that is long and narrow	a measuring instrument for measuring and indicating a quantity such as the thickness of wire or the amount of rain etc.
the linear extent in space from one end to the other; the longest dimension of something that is fixed in place	the distance between the rails of a railway or between the wheels of a train
continuance in time	the thickness of wire
the property of being the extent of something from beginning to end	diameter of a tube or gun barrel
size of the gap between two places	accepted or approved instance or example of a quantity or quality against which others are judged or measured or compared

length (verb)	gauge (verb)
	measure precisely and against a standard
	adapt to a specified measurement
	mix in specific proportions
	judge tentatively or form an estimate of (quantities or time)
	determine the capacity, volume, or contents of by measurement and calculation
	rub to a uniform size