What is 4. To cover or furnish with a plate, or with whatever will add strength, force, security, or efficiency; as, to arm the hit of a sword; to arm a hook in angling called?

arm — 4. To cover or furnish with a plate, or with whatever will add strength, force, security, or efficiency; as, to arm the hit of a sword; to arm a hook in angling. (Webster's 1913.)