WordNet Dictionary
Webster's 1913 Dictionary\Ex`e*cu"tion*er\, n. 1. One who executes; an executer. --Bacon. 2. One who puts to death in conformity to legal warrant, as a hangman.
Easton Bible Dictionary(Mark 6:27). Instead of the Greek word, Mark here uses a Latin word, speculator, which literally means "a scout," "a spy," and at length came to denote one of the armed bodyguard of the emperor. Herod Antipas, in imitation of the emperor, had in attendance on him a company of speculatores. They were sometimes employed as executioners, but this was a mere accident of their office. (See MARK, GOSPEL OF.)