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]

Moby Thesaurus II by Grady Ward, 1.0:

36 Moby Thesaurus words for "pontiff":
   Grand Penitentiary, Holy Father, abuna, antipope, archbishop,
   archdeacon, archpriest, bishop, bishop coadjutor, canon, cardinal,
   cardinal bishop, cardinal deacon, cardinal priest, chaplain,
   coadjutor, curate, dean, diocesan, ecclesiarch, exarch, hierarch,
   high priest, metropolitan, papa, patriarch, penitentiary, pope,
   prebendary, prelate, primate, rector, rural dean, subdean,
   suffragan, vicar