What is "to assume the calotte"

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:

1. Such a cap, worn by English serjeants at law.

2. Such a cap, worn by the French cavalry under their helmets.

3. Such a cap, worn by the clergy of the Roman Catholic Church.

   To assume the calotte, to become a priest.