sheath vs neurilemma

sheath and neurilemma both are nouns.

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

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

sheath: an enveloping structure or covering enclosing an animal or plant organ or part
neurilemma: thin membranous sheath around a nerve fiber

Other hyponyms of sheath include theca, lorica, medullary sheath, myelin sheath, neurolemma, husk.

sheath (noun)	neurilemma (noun)
a protective covering (as for a knife or sword)	thin membranous sheath around a nerve fiber
a dress suitable for formal occasions
an enveloping structure or covering enclosing an animal or plant organ or part