raise vs improve

raise is a noun but improve is not a noun.

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

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

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

raise (noun)	improve (noun)
the act of raising something
increasing the size of a bet (as in poker)
the amount a salary is increased
an upward slope or grade (as in a road)

raise (verb)	improve (verb)
cause to become alive again	get better
increase the level of	to make better
raise the level or amount of something
raise in rank or condition
invigorate or heighten
put an end to
bring (a surface or a design) into relief and cause to project
multiply (a number) by itself a specified number of times: 8 is 2 raised to the power 3
cause to be heard or known; express or utter
put forward for consideration or discussion
activate or stir up
establish radio communications with
pronounce (vowels) by bringing the tongue closer to the roof of the mouth
cause to assemble or enlist in military
bet more than the previous player
bid (one's partner's suit) at a higher level
summon into action or bring into existence, often as if by magic
construct, build, or erect
cultivate by growing, often involving improvements by means of agricultural techniques
create a disturbance, especially by making a great noise
call forth (emotions, feelings, and responses)
raise from a lower to a higher position
cause to puff up with a leaven
move upwards
collect funds for a specific purpose
look after a child until it is an adult
give a promotion to or assign to a higher position
register formally as a participant or member