meter vs power meter

meter and power meter both are nouns.

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

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

meter (noun)	power meter (noun)
any of various measuring instruments for measuring a quantity	a meter for measuring the amount of electric power used
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)

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