Pontifex MaximusPronunciation: /ˈmaksɪməs/Definition of Pontifex Maximus noun (in ancient Rome) the head of the principal college of priests. (in the Roman Catholic Church) a title of the Pope. Origin:Maximus, superlative of Latin magnus 'great'Pontifex Maximus in other Oxford dictionaries Definition of Pontifex Maximus in the US English dictionary