ASS (O.E. assa; Lat. asinus), a common name (the synonym "donkey" is supposed to be derived either by analogy from "monkey," or from the Christian name Duncan; cf. Neddy, Jack, Dicky, etc.) for different varieties of the sub-genus Asinus, belonging to the horse tribe, and especially for the domestic ass; it differs from the horse in its smaller size, long ears, the character of its tail, fur and markings, and its proverbial dulness and obstinacy. The ancient Egyptians symbolized an ignorant person by the head and ears of an ass, and the Romans thought it a bad omen to meet one. In the middle ages the Germans of Westphalia made the ass the symbol of St Thomas, the incredulous apostle; the boy who was last to enter school on St Thomas' day was called the "Ass Thomas" (Gubernatis's Zoological Mythology, i. 362). The foolishness and obstinacy of the ass has caused the name to be transferred metaphorically to human beings; and the fifth proposition of Book i. of Euclid is known as the Pons Asinorum, bridge of asses.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)