armguard vs protective cover

armguard and protective cover both are nouns.

Word	Noun	Adjective	Verb	Adverb
armguard	Yes	No	No	No
protective cover	Yes	No	No	No

As nouns, protective cover is a hypernym of armguard; that is, protective cover is a word with a broader meaning than armguard:

armguard: a protective covering for the wrist or arm that is used in archery and fencing and other sports
protective cover: a covering that is intend to protect from damage or injury

Other hypernyms of armguard include protection, protective covering.

armguard (noun)	protective cover (noun)
a protective covering for the wrist or arm that is used in archery and fencing and other sports	a covering that is intend to protect from damage or injury