execution speed vs fastness

execution speed and fastness both are nouns.

Word	Noun	Adjective	Verb	Adverb
execution speed	Yes	No	No	No
fastness	Yes	No	No	No

As nouns, fastness is a hypernym of execution speed; that is, fastness is a word with a broader meaning than execution speed:

execution speed: (computer science) the speed with which a computational device can execute instructions; measured in MIPS
fastness: a rate (usually rapid) at which something happens

Other hypernyms of execution speed include speed, swiftness.

execution speed (noun)	fastness (noun)
(computer science) the speed with which a computational device can execute instructions; measured in MIPS	a strongly fortified defensive structure
	a rate (usually rapid) at which something happens
	the quality of being fixed in place as by some firm attachment