epicardium vs serous membrane

epicardium and serous membrane both are nouns.

Word	Noun	Adjective	Verb	Adverb
epicardium	Yes	No	No	No
serous membrane	Yes	No	No	No

As nouns, serous membrane is a hypernym of epicardium; that is, serous membrane is a word with a broader meaning than epicardium:

epicardium: the innermost of the two layers of the pericardium
serous membrane: a thin membrane lining the closed cavities of the body; has two layers with a space between that is filled with serous fluid

Other hypernyms of epicardium include serosa.

epicardium (noun)	serous membrane (noun)
the innermost of the two layers of the pericardium	a thin membrane lining the closed cavities of the body; has two layers with a space between that is filled with serous fluid