mammary gland vs dug

mammary gland and dug both are nouns.

Word	Noun	Adjective	Verb	Adverb
mammary gland	Yes	No	No	No
dug	Yes	No	No	No

As nouns, dug is a hyponym of mammary gland; that is, dug is a word with a more specific, narrower meaning than mammary gland:

Other hyponyms of mammary gland include bag, udder, boob, bosom, breast, knocker, tit, titty.

mammary gland (noun)	dug (noun)
milk-secreting organ of female mammals	an udder or breast or teat