Unagi-meshi is an abbreviation for "unagi donburi meshi (a bowl of boiled rice topped with broiled eel)," according to Morisada Manko (a kind of encyclopedia of folkways and other affairs in the Edo period, written by Morisada KITAGAWA), which is regarded as a basic document on the history of early modern folkways.
近世風俗史の基本文献とされている守貞謾稿によると、鰻飯は「鰻丼飯」の略。