sea cow vs dugong

sea cow and dugong both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea cow	Yes	No	No	No
dugong	Yes	No	No	No

As nouns, dugong is a hyponym of sea cow; that is, dugong is a word with a more specific, narrower meaning than sea cow:

sea cow: any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs
dugong: sirenian tusked mammal found from eastern Africa to Australia; the flat tail is bilobate

sea cow (noun)	dugong (noun)
any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs	sirenian tusked mammal found from eastern Africa to Australia; the flat tail is bilobate