milk vs mother's milk

milk and mother's milk both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk	Yes	No	Yes	No
mother's milk	Yes	No	No	No

As nouns, mother's milk is a hyponym of milk; that is, mother's milk is a word with a more specific, narrower meaning than milk:

Other hyponyms of milk include colostrum, foremilk.

milk (noun)	mother's milk (noun)
produced by mammary glands of female mammals for feeding their young	milk secreted by a woman who has recently given birth
a white nutritious liquid secreted by mammals and used as food by human beings
any of several nutritive milklike liquids

milk (verb)	mother's milk (verb)
take milk from female mammals
add milk to
exploit as much as possible