Origins
A duke is in origin a
leader, Latin
dux (stem
duc-). The same root appears in
seduce (lead away),
duct,
douche (originally piped water) etc. The
Germanic form appears in English
tow and
tug. The sense '
war leader' is made explicit in
Old English here-toga, and still exists as the German for duke,
Herzog.
King Arthur was called
dux bellorum, 'leader of wars'.
Territorial titles of duke existed across Europe by the time of the Norman Conquest, for William I was Duke of Normandy when he seized the English throne, but there were no English dukes at that time. The first was Duke of Cornwall, a title conferred in 1337 on the king's eldest son. Other titles followed: Lancaster 1351, then Clarence, York, Gloucester, Bedford, and Somerset, all on members of the immediate royal family. The Duke of Buckingham created in 1444 was royal only on his mother's side, and the Duke of Norfolk 1483 was not royal.
To this day titles such as York and Gloucester are conferred on royal sons. These royal dukes rank higher than other dukes. They only last for two generations, then revert back to the Crown to be newly conferred on a son in the royal family. In contrast, the Duke of Norfolk still exists from the 1483 creation and he is known as the Premier Duke of England, and duke being the highest rank, he is Premier Peer.
In Scotland royal dukedoms were first conferred in 1398, the Dukes of Rothesay and Albany. Today the Prince of Wales is also the Duke of Rothesay. The (non-royal) Premier Duke of Scotland is the Duke of Hamilton, created 1643, and the Irish one is Leinster, 1766.
Style and precedence
The title of duke is the highest of the five ranks of
peerage in the British system, and this generally matches the Continental equivalents: French
duc, Italian
duca (also Mussolini's
duce), Spanish and Portuguese
duque, German
Herzog, Dutch
hertog etc. But on the Continent some are styled
Grand Duke (as in
Luxembourg) or (in Austria)
Archduke. In
Venice and
Genoa the ruler was called
doge, ultimately the same word.
The wife of a duke is a duchess (until about 1800 more usually spelt dutchess). On the Continent there have been duchesses in their own right, succeeding their father or husband as ruler, but I don't know that there ever has been an actual duchess in Britain. (Ah, wait, yes there has: both the Duke of Marlborough and the Duke of Fife were succeeded by daughters.) The style of duchess is normally a courtesy title for a duke's wife.
The eldest son of a duke is by courtesy styled by his father's second title. This should preferably be one of the next rank down, Marquess, but if his father doesn't hold a marquessate the son is known by whatever lesser title is available, though ranks as a marquess in precedence. Other children of a duke are styled Lord or Lady with both forename and surname, e.g. the Duke of Wellington's eldest son is called Marquess of Douro and his other children might be Lord John Wellesley or Lady Anne Wellesley.
The land of a duke is called a duchy, and the title is a dukedom. The -ch- forms duchess and duchy are pronounced like "Dutch", not with the "you" sound of duke. The Italian for duchy, ducato, gives us the coin name ducat, first issued by Roger II of Naples (Duke of Apulia 1128-1154).
The formal manner of address to a duke is "Your Grace", and an envelope would be addressed to "His Grace the Duke of...", and the letter headed "My Lord Duke", and this is what you would expect in a novel set in the past; but today the formal styles are less used. You would socially write "The Duke of..." and "Dear Duke", and address him as (this horrified me but it says so in Whitaker's Almanac) "Duke". I must stress do not do this if you think you're the next Georgette Heyer! Use formal styles for anything in the past.
Accoutrements
A ducal
robe has four bars of
ermine on each side. Peers have two kinds of robe, a
Coronation robe of crimson velvet lined with
miniver, and a
Parliamentary robe (for those now-gone days when they all sat in the
House of Lords) of scarlet lined with
taffeta.
A duke's coronet is a golden circlet with eight strawberry leaves around it (pointing up from it). The coronet itself is chased as if in the form of jewels (like a royal crown) but is not actually jewelled. It has a purple cap (lined ermine) in real life and a crimson one in heraldic representation. It has a gold tassel on top. The strawberry leaves are what distinguish a ducal coronet from other ranks'.
In heraldry there is a convention that a coronet of only four strawberry leaves (so you see one in front and two half-on) is termed a ducal coronet (or ducal crest coronet). It was formerly granted in some cases as the support from which the crest issues, though a wreath is now always used for this. The crest is the little bit that sits over the helmet over the shield.
Today
Today in Britain there are five royal dukes.
Prince Philip was created Duke of Edinburgh on his marriage to the then Princess Elizabeth in 1947. In this dukedom he will be succeeded by their third son, currently
Earl of Wessex (Prince Edward). The Prince of Wales is automatically Duke of Cornwall and Duke of Rothesay. Prince Andrew is Duke of York. Two of the Queen's cousins are also royal dukes, those of Gloucester and Kent. Since they are each the second of the present creation, being sons of sons of George V, their titles will cease to exist with them.
Other royal dukedoms not currently in use include Cumberland, Albany, Clarence, Sussex, and that of Windsor, created for the former king Edward VIII. The Duchy of Lancaster has a continuing legal personality but is now permanently held by the Crown.
Outside royalty there are 25 dukes, of whom ten hold English titles, six Scottish, and two Irish. The rest are creations since the union of the crowns: dukes of Great Britain from 1707 and of the United Kingdom from 1801. Because they are less ancient they rank a little below those of England or Scotland. The English ones are Beaufort, Bedford (not the original creation I mentioned in the history section), Devonshire, Grafton, Marlborough, Norfolk, Richmond, Rutland, St Albans, and Somerset. The Britannica calls Marlborough a Great Britain creation but I think they're wrong, as it dates from 1702. There are several more dukedoms than that since some Scottish dukes hold two apiece, such as the Duke of Buccleuch and Queensberry. The Scottish duke of Argyll also holds a UK dukedom of the same name.
SOURCES INCLUDE:
The OED
W.W. Skeat, A Concise Etymological Dictionary of the English Language, Oxford 1882
A.C. Fox-Davies, A Complete Guide to Heraldry, Thomas Nelson & Sons, 1909
Whitaker's Almanac
Encyclopaedia Britannica