Why is the ninth month called September?
c.1300, an order of knighthood, originally in reference to one who could lead his men into battle under his own banner. Later it meant one who received rank for valiant deeds done in the king's presence in battle. Also "a small banner" (c.1300).
a European medieval knight privileged to display in the field a square banner (as distinct from the tapering pennon of a simple knight). The term was used in countries of French and English speech from the 13th to the 16th century. In 13th-century England any commander of a troop of 10 or more lances who was not a count or an earl was usually a banneret. Later, in both England and France, the style became a title of honour, conferred for distinguished military service. There is no connection between the style of banneret and the baronetage (hereditary dignity) established in England by King James I in 1611.