addition vs increase

addition and increase both are nouns.

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

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

Other hypernyms of addition include step-up.

As nouns, addition and increase are synonyms defined as:

Other synonyms of addition include gain.

addition (noun)	increase (noun)
the arithmetic operation of summing; calculating the sum of two or more numbers	the act of increasing something
the act of adding one thing to another	the amount by which something increases
a component that is added to something to improve it	a change resulting in an increase
a suburban area laid out in streets and lots for a future residential area	a process of becoming larger or longer or more numerous or more important
something added to what you already have	a quantity that is added
a quantity that is added

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