arm vs rearm

arm is a noun but rearm is not a noun.

Word	Noun	Adjective	Verb	Adverb
arm	Yes	No	Yes	No
rearm	No	No	Yes	No

As verbs, rearm is a hyponym of arm; that is, rearm is a word with a more specific, narrower meaning than arm:

Other hyponyms of arm include re-arm, forearm.

As verbs, rearm is a hyponym of arm; that is, rearm is a word with a more specific, narrower meaning than arm:

Other hyponyms of arm include munition.

arm (noun)	rearm (noun)
the part of a garment that is attached at the armhole and that provides a cloth covering for the arm
any instrument or instrumentality used in fighting or hunting
the part of an armchair or sofa that supports the elbow and forearm of a seated person
any projection that is thought to resemble a human arm
a human limb; technically the part of the superior limb between the shoulder and the elbow but commonly used to refer to the whole superior limb
a division of some larger or more complex organization

arm (verb)	rearm (verb)
prepare oneself for a military confrontation	arm anew
supply with arms	arm again