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).
Peerages in the United Kingdom
The term "peerage" can be used both collectively to refer to the entire body of nobles (or a subdivision thereof), and individually to refer to a specific title (modern English language-style using an initial capital in the former case but not the latter). British peerage title holders are termed peers of the Realm.