body armor vs cataphract

body armor and cataphract both are nouns.

Word	Noun	Adjective	Verb	Adverb
body armor	Yes	No	No	No
cataphract	Yes	No	No	No

As nouns, body armor and cataphract are synonyms defined as:

Other synonyms of body armor include body armour, coat of mail, suit of armor, suit of armour.

body armor (noun)	cataphract (noun)
armor that protects the wearer's whole body	armor that protects the wearer's whole body