Vincent's NT Word Studies
27. Mark's favorite straightway. The king is prompt in his response.Executioner (spekoulatora). One of Mark's Latin words, speculator. A speculator was a guardsman, whose business it was to watch or spy out (speculari). It came gradually to denote one of the armed body-guard of the Roman emperor. Thus Suetonius says of Claudius that he did not dare to attend banquets unless his speculatores with their lances surrounded him. Seneca uses the word in the sense of executioner. "He met the executioners (speculatoribus), declared that he had nothing to say against the execution of the sentence, and then stretched out his neck." Herod imitated the manners of the Roman court, and was attended by a company of speculatores, though it was not their distinctive office to act as executioners. Wyc. renders man-killer, and Tynd. hangman.
Robertson's NT Word Studies
6:27 {A soldier of his guard} (spekoulatora). Latin word _speculator_. A spy, scout, lookout, and often executioner. It was used of the bodyguard of the Roman emperor and so for one of Herod's spies. He was used to do errands of this sort and it was soon done. It was a gruesome job, but he soon brought John's head to the damsel, apparently in the presence of all, and she took it to her mother. this miserable Tetrarch, the slave of Herodias, was now the slave of his fears. He is haunted by the ghost of John and shudders at the reports of the work of Jesus.