Mon·sieur (mə-syɶ') n.
pl.Mes·sieurs (mā-syɶ', měs'ərz)
Abbr. M. Used as a courtesy title before the surname, full name, or professional title of a man in a French-speaking area: Monsieur Cartier; Monsieur Jacques Cartier.
monsieur Used as a form of polite address for a man in a French-speaking area.
[French, from Old French : mon, my (from Latin meum, accusative of meus; see me-1 in Indo-European roots) + sieur, lord, sir (from Vulgar Latin *seiorem, accusative of *seior; see sire).]
1512, from Fr., from mon sieur "my lord," from sieur "lord," shortened form of seigneur (see monseigneur) It was the historical title for the second son or next younger brother of the king of France.