A coronet is a small crown consisting of ornaments fixed on a metal ring. Unlike a crown, a coronet never has arches.
The word stems from the Old French coronete, a diminutive of co(u)ronne ("crown"), itself from the Latin corona (also "wreath").
Traditionally, such headgear is – as indicated by the German equivalent Adelskrone (literally "crown of nobility") – used by nobles and by princes and princesses in their coats of arms, rather than by monarchs, for whom the word crown is customarily reserved in formal English, while many languages have no such terminological distinction. Other than a crown, a coronet shows the rank of the respective noble. Hence, in German language there is also the term Rangkrone.
For equivalents, both physical and emblematic, in other languages and cultures, see under crown (headgear).
The main use is now actually not on the head (indeed, many people entitled to a coronet never have one made; the same even applies to some monarchs' crowns, as in Belgium) but as a rank symbol in heraldry, adorning a coat of arms.
In the peerage of the United Kingdom, the design of a coronet shows the rank of its owner, as in German, French and various other heraldic traditions.
Since a person entitled to wear a coronet customarily displays it in his or her coat of arms above the shield and below the helm and crest, this can provide a useful clue as to the owner of a given coat of arms. In Canadian heraldry, descendants of the United Empire Loyalists are entitled to use a Loyalist military coronet (for descendants of members of Loyalist regiments) or Loyalist civil coronet (for others) in their arms.
Members of the British Royal Family have coronets on their coats of arms and may wear them at coronations. They were made, according to regulations made by King Charles II in 1661, shortly after his return from exile in France (getting a taste for its lavish court style; Louis XIV started monumental work at Versailles that year) during the Restoration. They vary depending upon the prince's relationship to the monarch. Occasionally, additional royal warrants vary the designs for individuals.
There is evidence to support the wearing of coronets amongst the Welsh royalty and nobility, particularly in the Kingdom of Gwynedd. Llywelyn's coronet was for a while kept with the English crown jewels.
Considering the highly religious nature of the Holy Roman Empire, one can say that, except for the short-lived Napoleonic states, no continental secular system of heraldry historically was so neatly regulated as under the British crown. Still, there are often traditions (often connected to the Holy Roman Empire, e.g., those in Sweden, Denmark or Russia) that include the use of crown and coronets. While most languages do not have a specific term for coronets, but simply use the word meaning crown, it is possible to determine which of those crowns are for peerage or lower-level use, and thus can by analogy be called coronets.
Precisely because there are many traditions and more variation within some of these, there is a plethora of continental coronet types. Indeed there are also some coronets for positions that do not exist or entitle one to a coronet in the Commonwealth tradition.
Such a case in French ("old", i.e., royal era) heraldry, where coronets of rank did not come into use before the 16th century, is the vidame, whose coronet (illustrated) is a metal circle mounted with three visible crosses (no physical headgear of this type known).
Often, coronets are substituted by helmets, or only worn on a helmet.