verb
BAD : For two weeks' work, I gain about 700,000 yen.
GOOD : For two weeks' work, I earn about 700,000 yen.
BAD : Without a job it's impossible to gain any money.
GOOD : Without a job it's impossible to earn any money.
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earn or (especially in informal styles) get / make (a sum of) money by going to work, from investments, etc (NOT gain ): 'She earns $4,000 a month.'