From the Hebrew name אֵיתָן ('Eitan) meaning "solid, enduring, firm". In the Old Testament this name is borne by a few minor characters, including the wise man Ethan the Ezrahite, supposedly the author of Psalm 89.
After the Protestant Reformation it was occasionally used as a given name in the English-speaking world, and it became somewhat common in America due to the fame of the revolutionary Ethan Allen (1738-1789). It only became popular towards the end of the 20th century. It is the name of the main character in Edith Wharton's novel 'Ethan Frome' (1911), about a man in love with his wife's cousin.