increase vs gain

increase and gain both are nouns.

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

As nouns, gain is a hyponym of increase; that is, gain is a word with a more specific, narrower meaning than increase:

increase: the amount by which something increases
gain: the amount of increase in signal power or voltage or current expressed as the ratio of output to input

As nouns, increase and gain are synonyms defined as:

Other synonyms of increase include addition.

As verbs, gain is a hyponym of increase; that is, gain is a word with a more specific, narrower meaning than increase:

increase (noun)	gain (noun)
the act of increasing something	the amount of increase in signal power or voltage or current expressed as the ratio of output to input
the amount by which something increases	the advantageous quality of being beneficial
a change resulting in an increase	the amount by which the revenue of a business exceeds its cost of operating
a process of becoming larger or longer or more numerous or more important	a quantity that is added
a quantity that is added

increase (verb)	gain (verb)
become bigger or greater in amount	increase (one's body weight)
make bigger or more	rise in rate or price
	increase or develop
	obtain advantages, such as points, etc.
	reach a destination, either real or abstract
	earn on some commercial or business transaction; earn as salary or wages
	win something through one's efforts
	derive a benefit from
	obtain