Is John the Baptist a Christian Martyr?

Merriam-Webster defines *martyr* as "a person who voluntarily suffers death as the penalty of witnessing to and refusing to renounce a religion." John the Baptist did suffer death, the first known associate of Jesus to do so. But it does not seem that he suffered for refusing to renounce his religion, nor did he suffer for witnessing to Jesus. Instead, we are told that he was imprisoned and later beheaded because 'John said to Herod [Antipas], “It is not lawful for you to have your brother’s wife.”' (Mark 6:18) The issue was that according to Jewish law (Leviticus 20:21), a man must not marry a woman was divorced from his brother (as opposed to his widow). This was the situation between Herod Antipas and his brother, known both as Herod II and Herod Phillip. This being the case, it seems that John the Baptist died for the political offense of publicly criticizing the ruler. He may be seen as dying for refusing to renounce the particular Jewish law mentioned above, but not for his belief in Jesus. Jesus is not known to have ever mentioned the issue of Antipas' marriage. John is clearly a saint according to many Christian traditions. But do these traditions consider him a martyr of Christian faith? **The question: Is John the Baptist a Christian martyr? I am seeking information on this subject both from experts and from denominational perspectives.** ________________________ > note: I would appreciate help from the moderators in phrasing the > question in case it is thought to be opinion-based.