development vs improvement

development and improvement both are nouns.

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

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

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

development: a state in which things are improving; the result of developing (as in the early part of a game of chess)
improvement: a condition superior to an earlier condition

Other hypernyms of development include melioration.

development (noun)	improvement (noun)
act of improving by expanding or enlarging or refining	the act of improving something
the act of making some area of land or water more profitable or productive or useful	a change for the better; progress in development
(music) the section of a composition or movement (especially in sonata form) where the major musical themes are developed and elaborated	a condition superior to an earlier condition
a recent event that has some relevance for the present situation
a district that has been developed to serve some purpose
processing a photosensitive material in order to make an image visible
(biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level
a process in which something passes by degrees to a different stage (especially a more advanced or mature stage)
a state in which things are improving; the result of developing (as in the early part of a game of chess)