speed vs brisk up

speed is a noun but brisk up is not a noun.

Word	Noun	Adjective	Verb	Adverb
speed	Yes	No	Yes	No
brisk up	No	No	Yes	No

As verbs, brisk up is a hyponym of speed; that is, brisk up is a word with a more specific, narrower meaning than speed:

Other hyponyms of speed include brisk, brisken.

speed (noun)	brisk up (noun)
changing location rapidly
a central nervous system stimulant that increases energy and decreases appetite; used to treat narcolepsy and some forms of depression
a rate (usually rapid) at which something happens
the ratio of the focal length to the diameter of a (camera) lens system
distance travelled per unit time

speed (verb)	brisk up (verb)
move faster	become brisk
cause to move faster
move very fast
travel at an excessive or illegal velocity
move hurridly