gain vs take advantage

gain is a noun but take advantage is not a noun.

Word	Noun	Adjective	Verb	Adverb
gain	Yes	No	Yes	No
take advantage	No	No	Yes	No

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

Other hyponyms of gain include cash in on, profiteer, capitalise, capitalize, pyramid, clear, net, sack, sack up.

gain (noun)	take advantage (noun)
the amount of increase in signal power or voltage or current expressed as the ratio of output to input
the advantageous quality of being beneficial
the amount by which the revenue of a business exceeds its cost of operating
a quantity that is added

gain (verb)	take advantage (verb)
increase (one's body weight)	draw advantages from
rise in rate or price	make excessive use of
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