The Collaborative International Dictionary of English v.0.48:

Mantelletta \Man`tel*let"ta\, n. [It. mantelletta. See
   Mantelet.] (R. C. Ch.)
   A silk or woolen vestment without sleeves worn by cardinals,
   bishops, abbots, and the prelates of the Roman court. It has
   a low collar, is fastened in front, and reaches almost to the
   knees.
   [Webster 1913 Suppl.]