mph vs meter reading

mph and meter reading both are nouns.

Word	Noun	Adjective	Verb	Adverb
mph	Yes	No	No	No
meter reading	Yes	No	No	No

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

mph: a speedometer reading for the momentary rate of travel
meter reading: a datum about some physical state that is presented to a user by a meter or similar instrument

Other hypernyms of mph include indication, reading.

mph (noun)	meter reading (noun)
a speedometer reading for the momentary rate of travel	the act of measuring with meters or similar instruments
the ratio of the distance traveled (in miles) to the time spent traveling (in hours)	a datum about some physical state that is presented to a user by a meter or similar instrument