slowness vs pace

slowness and pace both are nouns.

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

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

Other hypernyms of slowness include rate.

slowness (noun)	pace (noun)
a rate demonstrating an absence of haste or hurry	a step in walking or running
lack of normal development of intellectual capacities	the relative speed of progress or change
unskillfulness resulting from a lack of training	a unit of length equal to 3 feet; defined as 91.44 centimeters; originally taken to be the average length of a stride
	the distance covered by a step
	the rate of moving (especially walking or running)
	the rate of some repeating event