The month after marriage, or so much of it as is spent away from home; so called from the practice of the ancient Teutons of drinking honey-wine (hydromel) for thirty days after marriage. Attila, the Hun, indulged so freely in hydromel at his wedding-feast that he died.
“It was the custom of the higher order of the Teutons … to drink mead or metheglin (a beverage made from honey) for thirty days after every wedding. From this comes the expression ‘to spend the honeymoon.ʹ”—W. Pulleyn: Etymological Compendium, § 9, p. 142.