water ox vs Old World buffalo

water ox and Old World buffalo both are nouns.

Word	Noun	Adjective	Verb	Adverb
water ox	Yes	No	No	No
Old World buffalo	Yes	No	No	No

As nouns, Old World buffalo is a hypernym of water ox; that is, Old World buffalo is a word with a broader meaning than water ox:

water ox: an Asian buffalo that is often domesticated for use as a draft animal
Old World buffalo: any of several Old World animals resembling oxen including, e.g., water buffalo, Cape buffalo

Other hypernyms of water ox include buffalo.

water ox (noun)	Old World buffalo (noun)
an Asian buffalo that is often domesticated for use as a draft animal	any of several Old World animals resembling oxen including, e.g., water buffalo, Cape buffalo