noun
1
BAD : The plan to reduce the arm forces is strongly opposed.
GOOD : The plan to reduce the armed forces is strongly opposed.
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armed = having one or more weapons: 'Both hijackers are believed to be armed.'
the armed forces = (a country's) army, navy, and air force
2
BAD : She wouldn't stop crying until I held her on my arms.
GOOD : She wouldn't stop crying until I held her in my arms.
BAD : I shall never forget the day he died on my arms.
GOOD : I shall never forget the day he died in my arms.
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(hold sb/sth) in your arms (NOT on ): 'He had a great pile of books in his arms.'