Founding his study on semantic and formal analyses and using mostly Roman or Latin sources as well as incidentally Arab sources, the author revises the classical etymologies of alcaide and alcalde so as to provide new solutions to the problems still posed by the origins of these words. Thus, considering the earliest chronological occurences of the Arabic words qâ id and qâdi, and, on the other hand, the various ancient occurences of alcaide and alcalde, all these words are analysed, trying to find satisfactory etymologies, whether common or divergeing, able to throw a light on the circumstances which influenced the creation of the above mentioned Spanish words. Also, taking into account the existence of other words which can be considered as being similar to the words alcaide and alcalde, such as the Sicilian caitu and the Corsican capite, the author is led to the conclusion that alcaide and alcalde, as well as qâ‘id and qâdi, derive from the latin form *capitem.