Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

AFTER the death of Isaac, his sons divided their habitations respectively; nor did they retain what they had before; but Esau departed from the city of Hebron, and left it to his brother, and dwelt in Seir, and ruled over Idumea. He called the country by that name from himself, for he was named Adom; which appellation he got on the following occasion : - One day returning from the toil of hunting very hungry, (it was when he was a child in age,) he lighted on his brother when he was getting ready lentile-pottage for his dinner, which was of a very red color; on which account he the more earnestly longed for it, and desired him to give him some of it to eat: but he made advantage of his brother's hunger, and forced him to resign up to him his birthright; and he, being pinched with famine, resigned it up to him, under an oath. Whence it came, that, on account of the redness of this pottage, he was, in way of jest, by his contemporaries, called Adom, for the Hebrews call what is red Adom; and this was the name given to the country; but the Greeks gave it a more agreeable pronunciation, and named it Idumea.