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.

The pope.

Also Holy See, Pope, Holy Father. The head of the Roman Catholic Religion founded by Christ under St. Peter

the head of the Roman Catholic Church

a person who acts vaguely like a king in a church or a group of churches, who presumes that he has the authority to speak with overriding authority on all things, or on most things, in his dominion

Pontiff is a title of certain religious leaders. It comes from the Latin word pontifex, which literally means bridge-maker. It could therefore be construed to mean a bridge between God and humanity.