plate armour vs cataphract

plate armour and cataphract both are nouns.

Word	Noun	Adjective	Verb	Adverb
plate armour	Yes	No	No	No
cataphract	Yes	No	No	No

As nouns, cataphract is a hypernym of plate armour; that is, cataphract is a word with a broader meaning than plate armour:

plate armour: a historical type of personal armor made from iron or steel plates, which superseded mail during the 14th century.
cataphract: armor that protects the wearer's whole body

Other hypernyms of plate armour include body armor, body armour, coat of mail, suit of armor, suit of armour.

plate armour (noun)	cataphract (noun)
specially hardened steel plate used to protect fortifications or vehicles from enemy fire	armor that protects the wearer's whole body
a historical type of personal armor made from iron or steel plates, which superseded mail during the 14th century.