Synonyms for Arm (same or very similar meaning)
WordNet sense 1 (an administrative division of some larger or more complex organization):
branch, subdivision
WordNet sense 2 (any instrument or instrumentality used in fighting or hunting):
weapon, weapon system
WordNet sense 3 (the part of a garment that is attached at the armhole and that provides a cloth covering for the arm):
sleeve
WordNet sense 4 (any projection that is thought to resemble a human arm):
limb
WordNet sense 5 (prepare oneself for a military confrontation):
fortify, gird, build up
From the ODE community, based on WordNet
add/edit