c.1600, from French monseigneur (12c.), title of honor equivalent to "my lord," from mon "my" (from Latin meum) + seigneur "lord," from Latin seniorem, accusative of senior "older" (see senior (adj.)). Plural messeigneurs.
former French title, appearing without an adjoining proper name, used to refer to or address the dauphin, or grand dauphin, heir apparent to the crown. Monseigneur was first applied to Louis XIV's son Louis de France (d. 1711) and grandson Louis, duc de Bourgogne (d. 1712); later to Louis XV's son Louis de France (d. 1765); and finally to Louis XVI's son Louis (d. 1789). More generally, monseigneur was used as a title preceding the titles of dukes and other peers, marshals of France, ministers of state, councillors of state, and presidents of sovereign courts