slowness vs rate

slowness and rate both are nouns.

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

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

Other hypernyms of slowness include pace.

slowness (noun)	rate (noun)
a rate demonstrating an absence of haste or hurry	the relative speed of progress or change
lack of normal development of intellectual capacities	amount of a charge or payment relative to some basis
unskillfulness resulting from a lack of training	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

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