To assume the calotte

from The Collaborative International Dictionary of English v.0.48

Calotte \Ca*lotte"\, Callot \Cal"lot\, n. [F. calotte, dim. of
   cale a sort of flat cap. Cf. {Caul}.]
   A close cap without visor or brim. Especially:
   (a) Such a cap, worn by English serjeants at law.
   (b) Such a cap, worn by the French cavalry under their
       helmets.
   (c) Such a cap, worn by the clergy of the Roman Catholic
       Church.
       [1913 Webster]

   {To assume the calotte}, to become a priest.
      [1913 Webster]