ass vs donkey

ass and donkey both are nouns.

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

As nouns, donkey is a hyponym of ass; that is, donkey is a word with a more specific, narrower meaning than ass:

ass: hardy and sure-footed animal smaller and with longer ears than the horse
donkey: domestic beast of burden descended from the African wild ass; patient but stubborn

Other hyponyms of ass include domestic ass, Equus asinus, jack, jackass, jennet, jenny, jenny ass, wild ass.

ass (noun)	donkey (noun)
slang for sexual intercourse	domestic beast of burden descended from the African wild ass; patient but stubborn
hardy and sure-footed animal smaller and with longer ears than the horse	the symbol of the Democratic Party; introduced in cartoons by Thomas Nast in 1874
the fleshy part of the human body that you sit on
a pompous fool