Châtelain (Med. Lat. castellanus, from castellum, a castle) was originally merely the French equivalent of the English castellan, i.e. the commander of a castle.
With the growth of the feudal system, however, the title gained in France a special significance which it never acquired in England, as implying the jurisdiction of which the castle became the centre. The châtelain was originally, in Carolingian times, an official of the count; with the development of feudalism the office became a fief, and so ultimately hereditary. In this as in other respects the châtelain was the equivalent of the viscount; sometimes the two titles were combined, but more usually in those provinces where there were châtelains there were no viscounts, and vice versa.
The title châtelain continued also to be applied to the inferior officer, or concierge châtelain, who was merely a castellan in the English sense. The power and status of châtelains necessarily varied greatly at different periods and places. Usually their rank in the feudal hierarchy was equivalent to that of the simple sire (dominus), between the baron and the chevalier; but occasionally they were great nobles with an extensive jurisdiction, as in the Low Countries (see Burgrave).
This variation was most marked in the cities, where in the struggle for power that of the châtelain depended on the success with which he could assert himself against his feudal superior, lay or ecclesiastical, or, from the 12th century onwards, against the rising power of the communes. The châtellenie (casteliania), or jurisdiction of the châtelain, as a territorial division for certain judicial and administrative purposes, survived the disappearance of the title and office of the châtelain in France, and continued till the Revolution.
In modern parlance the term "châtelaine" usually refers to the wife of the owner, or the female owner of a large house or similar establishment. It may also refer to a housekeeper, or the keychain worn by a housekeeper.
In Canada, the wife of the Governor-General (the Viceregal consort of Canada) is referred to as the "Châtelaine of Rideau Hall".