Today is one of the oldest and most widespread feasts of the Christian liturgical tradition, the commemoration of the beheading of St John the Baptist. At Mass, the majority of rites, including the Roman, read the most complete account of this event among the Gospels, from St Mark, chapter 6, 17-29. At verse 27, when King Herod orders the Saint to be killed, the Latin reads as follows: “sed misso spiculatore præcepit afferri caput ejus in disco – but having sent the executioner, he commanded that his head be brought on a platter.”
The Latin word for “executioner” here, “speculator”, underwent a curious evolution. It is an agent noun from the deponent verb “speculari – to spy out, watch (for), observe, examine, explore”; in St Jerome’s translations of the Hebrew Old Testament, it is most often used to mean “a watchman.” In the Roman army, however, it came to mean a member of a reconnaissance unit, hence “a scout” or “a spy.” In the early years of the empire, such military scouts began to be employed as military adjutants, body-guards and couriers, and this is the sense most often employed by Suetonius. But they might also be used as executioners, and by the time St Mark wrote his Gospel in the middle of the 1st century, this sense was obviously well-known, since he writes the word in Greek, “σπεκουλάτωρα”, rather than translate it.
From a very early period, Latin-speaking Christians did not translate the Greek names of most ranks of the clergy, but adopted the Greek words as technical terms. Hence, “acolythos”, “diaconos” and “presbyteros” find their way into English through Latin as “acolyte”, “deacon” and “priest.” The name of the highest rank, “episcopos”, which literally means “overseer” (i.e. the one who oversees what is happening in the local church), also finds its way into English through Latin as “bishop”, but was also, rarely, translated as “speculator.” By the time this first appears in the 4th century, the Latinized form “episcopus” was already of very long-standing use, and we may reasonably speculate (ahem…) that the translated form “speculator” might have sounded very pretentious to the ordinary Latin-speaking Christian, just as it would be pretentious to call a bishop an “overseer” nowadays.