machmeter vs speedometer

machmeter and speedometer both are nouns.

Word	Noun	Adjective	Verb	Adverb
machmeter	Yes	No	No	No
speedometer	Yes	No	No	No

As nouns, speedometer is a hypernym of machmeter; that is, speedometer is a word with a broader meaning than machmeter:

machmeter: speedometer for measuring the speed of an aircraft relative to the speed of sound
speedometer: a meter fixed to a vehicle that measures and displays its speed

Other hypernyms of machmeter include speed indicator.

machmeter (noun)	speedometer (noun)
speedometer for measuring the speed of an aircraft relative to the speed of sound	a meter fixed to a vehicle that measures and displays its speed