Rule by one man or women; a king or queen.
Bouvier in his American Law Dictionary of 1856 added that a disadvantage of a monarchy is that:
“… the personal interests or inclinations of the monarch or his house are substituted for the public interest; that to the chance of birth is left what with rational beings certainly ought to be the result of reason and wisdom.”
A constitutional monarchy is a bit of an oxymoron but it does reflect the reality of a monarch having abdicated some of his or her powers by compact with the people or its representatives, within a constitutional document such as the Magna Carta.
Bouvier’s defined a monarchy as follows:
“(G)overnment which is ruled (really or theoretically) by one man, who is wholly set apart from all other members of the state (called his subjects)."
A monarchy is the opposite of a republic, the latter being government without king or queen.
Walter Bagehot (1826-1877) once said of a monarchy, in words hopefully dated:
“The best reason why monarchy is a strong government is that it is an intelligible government. The mass of mankind understand it, and they hardly anywhere in the world understand any other.”