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]
(..) -There's logic to what he's saying. -How does he know? My lot is there! Two or three years, it could be ten years! -We gain nothing by losing our heads! -Look at that well out there! Nobody's losing their heads. You have no business being here! Sit that woman down, sir! You can sit down. (..)2007 There Will Be Blood