strengthening vs increase

strengthening and increase both are nouns.

Word	Noun	Adjective	Verb	Adverb
strengthening	Yes	No	No	No
increase	Yes	No	Yes	No

As nouns, increase is a hypernym of strengthening; that is, increase is a word with a broader meaning than strengthening:

Other hypernyms of strengthening include step-up.

strengthening (noun)	increase (noun)
the act of increasing the strength of something	the act of increasing something
becoming stronger	the amount by which something increases
	a change resulting in an increase
	a process of becoming larger or longer or more numerous or more important
	a quantity that is added

strengthening (verb)	increase (verb)
	become bigger or greater in amount
	make bigger or more