The Collaborative International Dictionary of English v.0.48:

Pontiff \Pon"tiff\, n. [F. pontife, L. pontifex, -ficis; pons,
   pontis, a bridge (perhaps originally, a way, path) + facere
   to make. Cf. Pontoon.]
   A high priest. Especially:
   (a) One of the sacred college, in ancient Rome, which had the
       supreme jurisdiction over all matters of religion, at the
       head of which was the Pontifex Maximus. --Dr. W. Smith.
   (b) (Jewish Antiq.) The chief priest.
   (c) (R. C. Ch.) The pope.
       [1913 Webster]

WordNet (r) 3.0 (2006):

pontiff
    n 1: the head of the Roman Catholic Church [syn: pope,
         Catholic Pope, Roman Catholic Pope, pontiff, Holy
         Father, Vicar of Christ, Bishop of Rome]