What does "ass" mean?

Ass: A dull, heavy, stupid fellow; a dolt. Shak. Asses' Bridge. Etym: [L. pons asinorum.] The fifth proposition of the first book of Euclid, "The angles at the base of an isosceles triangle are equal to one another." [Sportive] "A schoolboy, stammering out his Asses' Bridge." F. Harrison. -- To make an ass of one's self, to do or say something very foolish or absurd.