Dukes in the United Kingdom
Duke, in the United Kingdom, is the highest-ranking hereditary title in all four peerages of the British Isles. A duke thus outranks all other holders of titles of nobility (marquess, earl, viscount and baron).
Peerage of France
The French word ' is equivalent to the English "peerage". The individual title, ' in French and "peer" in English, derives from the Latin "", "equal". It signifies those noblemen and prelates considered to be equal to the monarch in honour (even though they were his vassals), and it considers the monarch thus to be , or "first among equals".