fallboard vs protective cover

fallboard and protective cover both are nouns.

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

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

fallboard: the hinged protective covering that protects the keyboard of a piano when it is not being played
protective cover: a covering that is intend to protect from damage or injury

Other hypernyms of fallboard include protection, protective covering.

fallboard (noun)	protective cover (noun)
the hinged protective covering that protects the keyboard of a piano when it is not being played	a covering that is intend to protect from damage or injury