membrane vs endosteum

membrane and endosteum both are nouns.

Word	Noun	Adjective	Verb	Adverb
membrane	Yes	No	No	No
endosteum	Yes	No	No	No

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

membrane: a pliable sheet of tissue that covers or lines or connects the organs or cells of animals or plants
endosteum: vascular membrane that lines the inner surface of long bones

membrane (noun)	endosteum (noun)
a thin pliable sheet of material	vascular membrane that lines the inner surface of long bones
a pliable sheet of tissue that covers or lines or connects the organs or cells of animals or plants