emission vs rheum

emission and rheum both are nouns.

Word	Noun	Adjective	Verb	Adverb
emission	Yes	No	No	No
rheum	Yes	No	No	No

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

emission: a substance that is emitted or released
rheum: a watery discharge from the mucous membranes (especially from the eyes or nose)

Other hyponyms of emission include exudate, exudation, transudate, transudation, effluvium, vaginal discharge.

emission (noun)	rheum (noun)
the act of emitting; causing to flow forth	a watery discharge from the mucous membranes (especially from the eyes or nose)
the occurrence of a flow of water (as from a pipe)
the release of electrons from parent atoms
any of several bodily processes by which substances go out of the body
a substance that is emitted or released