The Collaborative International Dictionary of English v.0.48:

Monsignore \Mon`si*gno"re\, n.; pl. Monsignors. [It., my lord.
   Cf. Monseigneur.]
   My lord; -- an ecclesiastical dignity bestowed by the pope,
   entitling the bearer to social and domestic rank at the papal
   court. (Abbrev. Mgr.)
   [1913 Webster]