Sir is a formal honorific address in English for men, derived from Sire in the High Middle Ages. Both are derived from the old French "Sieur" (Lord), brought to England by the French-speaking Normans, and which now exist in French only as part of "Monsieur", with the equivalent "My Lord" in English. Traditionally, as governed by law and custom, Sir is used for men who are knights and belong to certain orders of chivalry, as well as later applied to baronets and other offices. As the female equivalent for knighthood is damehood, the suo jure female equivalent term is typically Dame. The wife of a knight or baronet tends to be addressed as Lady, although a few exceptions and interchanges of these uses exist.
Sir Thomas Troubridge, 1st Baronet, whose entitlement to use 'Sir' derived from his position as baronet
Emperor Taishō, a Stranger Knight of the Order of the Garter, who, as a foreign national, was not entitled to use the prefix 'Sir' (which as a sovereign monarch he would not have used in any case) but was permitted to post-nominally use KG
Chithira Thirunal Balarama Varma was the last surviving Knight Grand Commander of the Order of the Star of India.
A baronet or the female equivalent, a baronetess, is the holder of a baronetcy, a hereditary title awarded by the British Crown. The title of baronet is mentioned as early as the 14th century; however, in its current usage it was created by James I of England in 1611 as a means of raising funds for the crown.
Neck decoration for baronets of the United Kingdom, depicting the Red Hand of Ulster
Coat of arms of the Agnew baronets (1629) with the badge of a Baronet of Nova Scotia (Coat of arms of Nova Scotia) in chief
Coat of arms of the Agnew baronets (1895) with the badge of a Baronet of the United Kingdom (Red Hand of Ulster) in canton
