fortify vs build up

fortify and build up both are verbs.

Word	Noun	Adjective	Verb	Adverb
fortify	No	No	Yes	No
build up	No	No	Yes	No

As verbs, fortify and build up are synonyms defined as:

Other synonyms of fortify include arm, gird.

fortify (verb)	build up (verb)
add alcohol to (beverages)	form or accumulate steadily
make strong or stronger	enlarge, develop, or increase by degrees or in stages
add nutrients to	change the use of and make available or usable
prepare oneself for a military confrontation	bolster or strengthen
enclose by or as if by a fortification	prepare oneself for a military confrontation