mend vs improve

mend is a noun but improve is not a noun.

Word	Noun	Adjective	Verb	Adverb
mend	Yes	No	Yes	No
improve	No	No	Yes	No

As verbs, improve is a hypernym of mend; that is, improve is a word with a broader meaning than mend:

mend: restore by replacing a part or putting together what is torn or broken
improve: to make better

Other hypernyms of mend include ameliorate, amend, better, meliorate.

As verbs, improve is a hypernym of mend; that is, improve is a word with a broader meaning than mend:

Other hypernyms of mend include ameliorate, better, meliorate.

mend (noun)	improve (noun)
the act of putting something in working order again
sewing that repairs a worn or torn hole (especially in a garment)

mend (verb)	improve (verb)
restore by replacing a part or putting together what is torn or broken	get better
heal or recover	to make better