indicator vs fuel gauge

indicator and fuel gauge both are nouns.

Word	Noun	Adjective	Verb	Adverb
indicator	Yes	No	No	No
fuel gauge	Yes	No	No	No

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

indicator (noun)	fuel gauge (noun)
a device for showing the operating condition of some system	an indicator of the amount of fuel remaining in a vehicle
a number or ratio (a value on a scale of measurement) derived from a series of observed facts; can reveal relative changes as a function of time
a signal for attracting attention
(chemistry) a substance that changes color to indicate the presence of some ion or substance; can be used to indicate the completion of a chemical reaction or (in medicine) to test for a particular reaction