Mach number vs ratio

Mach number and ratio both are nouns.

Word	Noun	Adjective	Verb	Adverb
Mach number	Yes	No	No	No
ratio	Yes	No	No	No

As nouns, ratio is a hypernym of Mach number; that is, ratio is a word with a broader meaning than Mach number:

Mach number: the ratio of the speed of a moving body to the speed of sound
ratio: the relative magnitudes of two quantities (usually expressed as a quotient)

Mach number (noun)	ratio (noun)
the ratio of the speed of a moving body to the speed of sound	the relation between things (or parts of things) with respect to their comparative quantity, magnitude, or degree
	the relative magnitudes of two quantities (usually expressed as a quotient)