Meaning

noun the symbol of the Democratic Party; introduced in cartoons by Thomas Nast in 1874

noun domestic beast of burden descended from the African wild ass; patient but stubborn

originThe origin is uncertain. Originally a slang term from the late eighteenth century. Perhaps from Middle English *donekie (“a miniature dun horse”), a double diminutive of Middle English don, dun, dunne (a name for a dun horse), equivalent to modern English dun (“brownish grey colour”) + -ock (diminutive suffix) + -ie (diminutive suffix), or similarly formed from the given name Duncan. Compare…

Etymology from Wiktionary, CC BY-SA 3.0