They hope to make big 'gains' in Congress in the coming election. [=they hope that many more members of their party will be elected to Congress]
Her hard work 'gained' her their respect. [=she has gained their respect through hard work; they respect her now because of her hard work]
a stock that was one of the year's biggest 'gainers' [=one of the stocks that increased the most in value]
(..) Doc, what's the harm in bringing back some info on the future? We could place some bets. DOC: I didn't invent the time machine for financial gain! The intent is to gain a clearer perception of humanity. Our past, our future, the pitfalls, the possibilities... (..)1989 Back to the Future Part II