/ ˈɪnfəntri; NAmE / noun
[ C +sing./pl. v . ] soldiers who fight on foot :
infantry units
The infantry was / were guarding the bridge.
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WORD ORIGIN
late 16th cent.: from French infanterie , from Italian infanteria , from infante youth, infantryman, from Latin infant- unable to speak, from in- not + fant- speaking (from the verb fari ).