To obtain, acquire, or increase something; to reach a place or position.
From Old French 'gagner' (meaning to earn or win), probably from Germanic 'waidanjan' (to hunt or pursue). Evolved to mean acquiring anything of value.
The word 'gain' is related to 'hunt' and 'pursue' in its roots, which explains why we talk about 'gaining ground' in war—like chasing prey, you're pursuing territory or advantage.
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