sheath vs protective covering

sheath and protective covering both are nouns.

Word	Noun	Adjective	Verb	Adverb
sheath	Yes	No	No	No
protective covering	Yes	No	No	No

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

sheath: a protective covering (as for a knife or sword)
protective covering: a covering that is intend to protect from damage or injury

Other hypernyms of sheath include protection, protective cover.

sheath (noun)	protective covering (noun)
a protective covering (as for a knife or sword)	the tough natural covering of some organisms
a dress suitable for formal occasions	a covering that is intend to protect from damage or injury
an enveloping structure or covering enclosing an animal or plant organ or part