Battalion

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late 16th century: from French bataillon, from Italian battaglione, from battaglia ‘battle’, from Latin (see battle).

wiktionary

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From French bataillon.

etymonline

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battalion (n.)

1580s, from French bataillon (16c.), from Italian battaglione "battle squadron," from diminutive of Vulgar Latin *battalia "battle," from Latin bauttere "to beat" (see batter (v.)). Specific sense of "part of a regiment" is from 1708. The oft-repeated quote "God is on the side of the largest battalions" (with many variants) usually is attributed to 17c. French military genius and marshal Turenne:

Madame, lui répondit-il, ne vous y fiez pas: j'ay tôujours vû Dieu do coté des gros Batallions. [E.Boursault, 1702]