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]
(..) What do I say? What do I say? I will never forget what you said. You told me my wife's dying words. Your wife's last wish is for you to gain the courage to We found the source of the phone call. It's in the Clean Room. Waiting for instructions. What are you doing? (..)2016 Arrival
(..) The call sign for him is 'big domino'. Whatever Shang does, at least four other nations'll follow. - Louise, we have to gain ground today. - OK. - You have a vocabulary list for me? - I do. You're gonna teach them your name and Ian's? Yeah, so that we can learn their names, (..)2016 Arrival