re-arm vs build up

re-arm and build up both are verbs.

Word	Noun	Adjective	Verb	Adverb
re-arm	No	No	Yes	No
build up	No	No	Yes	No

As verbs, build up is a hypernym of re-arm; that is, build up is a word with a broader meaning than re-arm:

Other hypernyms of re-arm include arm, fortify, gird.

re-arm (verb)	build up (verb)
arm anew	form or accumulate steadily
	enlarge, develop, or increase by degrees or in stages
	change the use of and make available or usable
	bolster or strengthen
	prepare oneself for a military confrontation