rapidity vs rate

rapidity and rate both are nouns.

Word	Noun	Adjective	Verb	Adverb
rapidity	Yes	No	No	No
rate	Yes	No	Yes	No

As nouns, rate is a hypernym of rapidity; that is, rate is a word with a broader meaning than rapidity:

Other hypernyms of rapidity include pace.

rapidity (noun)	rate (noun)
a rate that is rapid	the relative speed of progress or change
	amount of a charge or payment relative to some basis
	a quantity or amount or measure considered as a proportion of another quantity or amount or measure
	a magnitude or frequency relative to a time unit

rapidity (verb)	rate (verb)
	assign a rank or rating to
	estimate the value of
	be worthy of or have a certain rating