liner vs protective cover

liner and protective cover both are nouns.

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

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

liner: a protective covering that protects an inside surface
protective cover: a covering that is intend to protect from damage or injury

Other hypernyms of liner include protection, protective covering.

liner (noun)	protective cover (noun)
(baseball) a hit that flies straight out from the batter	a covering that is intend to protect from damage or injury
a large commercial ship (especially one that carries passengers on a regular schedule)
a piece of cloth that is used as the inside surface of a garment
a protective covering that protects an inside surface