Monsieur \Mon*sieur"\, n.; pl. Messieurs. [F., fr. mon my + Sieur, abbrev. of seigneur lord. See Monseigneur.]

1. The common title of civility in France in speaking to, or of, a man; Mr. or Sir. [Represented by the abbreviation M. or Mons. in the singular, and by MM. or Messrs. in the plural.]

2. The oldest brother of the king of France.

3. A Frenchman. [Contemptuous] --Shak.

Source: Webster's Revised Unabridged Dictionary (1913)