weakening vs reduction

weakening and reduction both are nouns.

Word	Noun	Adjective	Verb	Adverb
weakening	Yes	Yes	No	No
reduction	Yes	No	No	No

As nouns, reduction is a hypernym of weakening; that is, reduction is a word with a broader meaning than weakening:

Other hypernyms of weakening include decrease, diminution, step-down.

weakening (noun)	reduction (noun)
the act of reducing the strength of something	the act of decreasing or reducing something
becoming weaker	the act of reducing complexity
	any process in which electrons are added to an atom or ion (as by removing oxygen or adding hydrogen); always occurs accompanied by oxidation of the reducing agent

weakening (adjective)	reduction (adjective)
causing debilitation
moderating by making pain or sorrow weaker