hone vs brush up

hone is a noun but brush up is not a noun.

Word	Noun	Adjective	Verb	Adverb
hone	Yes	No	Yes	No
brush up	No	No	Yes	No

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

Other hyponyms of hone include optimise, optimize, polish, polish up, round, round off.

hone (noun)	brush up (noun)
a whetstone made of fine gritstone; used for sharpening razors
a tool consisting of a number of fine abrasive slips held in a machine head, rotated and reciprocated to impart a smooth finish to cylinder bores, etc.

hone (verb)	brush up (verb)
make perfect or complete	bring to a highly developed, finished, or refined state
sharpen with a hone	refresh one's memory