voltmeter vs meter

voltmeter and meter both are nouns.

Word	Noun	Adjective	Verb	Adverb
voltmeter	Yes	No	No	No
meter	Yes	No	Yes	No

As nouns, meter is a hypernym of voltmeter; that is, meter is a word with a broader meaning than voltmeter:

voltmeter (noun)	meter (noun)
meter that measures the potential difference between two points	any of various measuring instruments for measuring a quantity
	rhythm as given by division into parts of equal duration
	(prosody) the accent in a metrical foot of verse
	the basic unit of length adopted under the Systeme International d'Unites (approximately 1.094 yards)

voltmeter (verb)	meter (verb)
	measure with a meter
	stamp with a meter indicating the postage