washboard vs protective cover

washboard and protective cover both are nouns.

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

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

washboard: protective covering consisting of a broad plank along a gunwale to keep water from splashing over the side
protective cover: a covering that is intend to protect from damage or injury

Other hypernyms of washboard include protection, protective covering.

washboard (noun)	protective cover (noun)
protective covering consisting of a broad plank along a gunwale to keep water from splashing over the side	a covering that is intend to protect from damage or injury
device consisting of a corrugated surface to scrub clothes on