An ass; or (less frequently) a mule.
A stupid or obstinate fellow; an ass.
domestic beast of burden descended from the African wild ass; patient but stubborn
a another species, similar yes, but he is NOT a longeared horse
A bad player or fish.
A term for a weak or foolish player.
a poor player also see fish.
Donkey or donk is a term of derision to refer to a bad player or a bad play. Sometimes you will hear someone say "I donked off all my chips with second pair" to indicate that they made an unwise bet or call.