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]
(..) But instead, what I'm proposing is... We start accelerating immediately to preserve velocity and gain even more. We don't intercept with earth at all... But we come close enough to get a gravity assist and adjust course. (..)2015 The Martian