The phrase "gain advantage" implies taking an upper hand over someone or something. There are different synonyms to express this meaning. For instance, the term "secure benefit" highlights the idea of obtaining an advantage that can guarantee positive outcomes. Another synonym that emphasizes a similar meaning is "attain leverage", pointing to the idea of having a strategic position that puts one in control. "Acquire edge" is an expression that suggests obtaining a competitive advantage by enhancing one's position through knowledge, skills, or resources. Lastly, "gain upper hand" is an idiomatic expression that emphasizes gaining an advantage over someone else. Regardless of which synonym one uses, the phrase essentially speaks to obtaining an advantage over one's opposition.