sheath vs holster

sheath and holster both are nouns.

Word	Noun	Adjective	Verb	Adverb
sheath	Yes	No	No	No
holster	Yes	No	No	No

As nouns, holster is a hyponym of sheath; that is, holster is a word with a more specific, narrower meaning than sheath:

Other hyponyms of sheath include aglet, aiglet, cot, fingerstall, scabbard.

sheath (noun)	holster (noun)
a protective covering (as for a knife or sword)	a sheath (usually leather) for carrying a handgun
a dress suitable for formal occasions	a belt with loops or slots for carrying small hand tools
an enveloping structure or covering enclosing an animal or plant organ or part