Large organized groups of soldiers, or any large group of people working together.
From French bataillon, from Italian battaglia (battle), from Latin battuere (to beat). The word traveled through Romance languages to describe military units organized for battle.
A battalion was originally just a 'battle-line'—the word literally means 'beat group'—but militaries standardized it into specific sizes, which is why the same word means different troop counts in different armies even today.
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