/ ˈɑːmi; NAmE ˈɑːrmi/ noun ( pl. -ies )
1.
[ C +sing./pl. v . ] a large organized group of soldiers who are trained to fight on land :
The two opposing armies faced each other across the battlefield.
2.
the army [ sing.+ sing./pl. v . ] the part of a country's armed forces that fights on land :
Her husband is in the army .
After leaving school, Mike went into the army .
an army officer
3.
[ C +sing./pl. v . ] a large number of people or things, especially when they are organized in some way or involved in a particular activity :
an army of advisers / volunteers
An army of ants marched across the path.
For more information see the Cultural Guide
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WORD ORIGIN
late Middle English : from Old French armee , from armata , feminine past participle of Latin armare to arm.