Monroe \m(o)-nroe, mon-roe\ as a boy's name is pronounced mun-ROH. It is of Scottish and Gaelic origin, and the meaning of Monroe is "mouth of the river Rotha, in Ireland". Originated as a surname for those who lived near the river's mouth. The fifth American President, James Monroe (19th century), was known for his Monroe Doctrine, which by forbidding foreign interference in the Americas, helped define the new country's place in the world. Novelist H.H. Munro.