a title of civility used by the French, in speaking to or of their equals, or those that are but little below them. Thus a duke or a marquis, speaking to an equal or inferior, uses the word Monsieur; and a mechanic speaking to a mechanic, gives him the same title: but nobody calls the French king Monsieur, except the children of France. The word is compounded of mon, "my," and sieur, "sir."

In France, the inscriptions of all letters run thus: A monsieur monsieur such-a-one. Monsieur absolutely used, is a title given to the second son of France, and to the king's brother.