Quick answer
Monroe is a boy/girl name meaning "from the mouth of the Roe".
Meaning and history
From a Scottish surname meaning "from the mouth of the Roe". The Roe is a river in Northern Ireland. Two famous bearers of the surname were American president James Monroe (1758-1831) and American actress Marilyn Monroe (1926-1962). As a given name it was mostly masculine in America until around 2009. It was already rising in popularity for girls when singer Mariah Carey gave it to her daughter born 2011 (though this probably helped accelerate it).
Notes and context
Usage: english