• PAX (noun). The noun PAX has 1 sense: 1. (Roman Catholic Church) a greeting signifying Christian love for those assisting at the Eucharist. Familiarity information: PAX used as a noun is very rare. PAX (noun). The noun PAX has 1 sense: 1. (Roman Catholic Church) a greeting signifying Christian love for those assisting at the Eucharist. Familiarity information: PAX used as a noun is very rare.