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]
(..) They asked you to spy on me, didn’t they? I don’t, uh– I don’t know what to say. Remember back to your early teachings. All who gain power are afraid to lose it. - Even the Jedi. - The Jedi use their power for good. Good is a point of view, Anakin. The Sith and the Jedi (..)2005 Star Wars: Episode III - Revenge of the Sith