coaster vs protective cover

coaster and protective cover both are nouns.

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

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

coaster: a covering (plate or mat) that protects the surface of a table (i.e., from the condensation on a cold glass or bottle)
protective cover: a covering that is intend to protect from damage or injury

Other hypernyms of coaster include protection, protective covering.

coaster (noun)	protective cover (noun)
a covering (plate or mat) that protects the surface of a table (i.e., from the condensation on a cold glass or bottle)	a covering that is intend to protect from damage or injury
someone who coasts
a resident of a coastal area