Recorded in many forms including Casa, Casereaux, Cazalet, and what seems to be the English derivatives of Caslett, Coslett, and Caslitt, this is a surname of Roman (Latin) origins, and found in particularly in the countries of Spain, France and Italy. The derivation is from the ancient pre 7th century word "casa" for which the original meaning was house, although this in itself probably referred not to any house, but to the most important house in the village or town, the one occupied by a chief or noble. The development in England appears to be from the Huguenot protestant refugee spelling of Cazelet or Caselet, which first seem to be recorded in the city of London at the end of the 17th century. This was the peak time for the arrival of the refugees fleeing the persecution by the Catholic King Louis X1V, and it is estimated that over fifty thousand such refugees passed into and through London upto 1750. Although many refugees retained the French spelling of their surname and some still do so today, the endless wars with France which did not end until 1815 at Waterloo, created a serious anti-French feeling that in turn caused many refugees to adopt an "English" spelling to their name, as we feel is the case here. Certainly the surviving church registers of the diocese of Greater London show a line of development which commences with (for instance) Peter Cazalet, at the church known as St Bartholomew Exchange on December 28th 1704, Jean Cazalet at the French Church, Threadneedle Street, on March 26th 1727, and then apparently to Thomas Coslett, who married Mary Stroud at St James church, Clerkenwell, on October 10th 1769.