repair vs improvement

repair and improvement both are nouns.

Word	Noun	Adjective	Verb	Adverb
repair	Yes	No	Yes	No
improvement	Yes	No	No	No

As nouns, improvement is a hypernym of repair; that is, improvement is a word with a broader meaning than repair:

repair (noun)	improvement (noun)
the act of putting something in working order again	the act of improving something
a frequently visited place	a change for the better; progress in development
a formal way of referring to the condition of something	a condition superior to an earlier condition

repair (verb)	improvement (verb)
give new life or energy to
restore by replacing a part or putting together what is torn or broken
set straight or right
move, travel, or proceed toward some place
make amends for; pay compensation for