mid-15c., "kiss of peace," from Latin pax (genitive pacis) "peace," in Ecclesiastical Latin, "kiss of peace" (see peace). Capitalized, Pax was the name of the Roman goddess of peace. Used by 1933 with adjectives from national names, on model of Pax Romana (e.g. Pax Britannica, 1872; Pax Americana, 1886, with reference to Latin America).
A passenger: There were twenty pax listed for the trip
[1970s+; apparently derived fr passenger as prexy is fr president]