milk cow vs milker

milk cow and milker both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk cow	Yes	No	No	No
milker	Yes	No	No	No

As nouns, milk cow and milker are synonyms defined as:

Other synonyms of milk cow include dairy cattle, dairy cow, milch cow, milcher.

milk cow (noun)	milker (noun)
cattle that are reared for their milk	cattle that are reared for their milk