milk whey vs serum

milk whey and serum both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk whey	Yes	No	No	No
serum	Yes	No	No	No

As nouns, serum is a hypernym of milk whey; that is, serum is a word with a broader meaning than milk whey:

milk whey: the serum or watery part of milk that is separated from the curd in making cheese
serum: an amber, watery fluid, rich in proteins, that separates out when blood coagulates

Other hypernyms of milk whey include blood serum.

milk whey (noun)	serum (noun)
the serum or watery part of milk that is separated from the curd in making cheese	an amber, watery fluid, rich in proteins, that separates out when blood coagulates