ass vs equid

ass and equid both are nouns.

Word	Noun	Adjective	Verb	Adverb
ass	Yes	No	No	No
equid	Yes	No	No	No

As nouns, equid is a hypernym of ass; that is, equid is a word with a broader meaning than ass:

ass: hardy and sure-footed animal smaller and with longer ears than the horse
equid: hoofed mammals having slender legs and a flat coat with a narrow mane along the back of the neck

Other hypernyms of ass include equine.

ass (noun)	equid (noun)
slang for sexual intercourse	hoofed mammals having slender legs and a flat coat with a narrow mane along the back of the neck
hardy and sure-footed animal smaller and with longer ears than the horse
the fleshy part of the human body that you sit on
a pompous fool