milk of magnesia vs purgative

milk of magnesia and purgative both are nouns.

Word	Noun	Adjective	Verb	Adverb
milk of magnesia	Yes	No	No	No
purgative	Yes	Yes	No	No

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

milk of magnesia: purgative consisting of a milky white liquid suspension of magnesium hydroxide; used as a laxative and (in smaller doses) as an antacid
purgative: a purging medicine; stimulates evacuation of the bowels

Other hypernyms of milk of magnesia include aperient, cathartic, physic.

milk of magnesia (noun)	purgative (noun)
purgative consisting of a milky white liquid suspension of magnesium hydroxide; used as a laxative and (in smaller doses) as an antacid	a purging medicine; stimulates evacuation of the bowels

milk of magnesia (adjective)	purgative (adjective)
	strongly laxative