A political party, not a religious organization, probably adherents of the Herodian dynasty, mentioned in the New Testament as plotting against Our Lord (Matthew 22; Mark 3).
The origin of Herod the Great is involved in obscurity, but it is certain that he was not of pure Jewish pedigree.
This fact and his cruelty made him odious to many Jews.
He ruled by the good will of Rome, which he drew to his side by bribes and adulation.
By the exile of Archelaus, son of Herod the Great, the Jews were made more subject to Rome.
Every Jew hated this foreign domination, but the more prudent veiled their true feelings, because of the power of Rome.
The Herodians are not believed to have borne any love to their alien subjugators, but they simulated loyalty to Rome in a hope thereby to restore the national kingdom under the Herodian dynasty.
Therefore, although the Pharisees detested the Herodians, the two bodies made common cause against Jesus.
It was the Herodians, sent by the Pharisees, who, in the discussion of the tribute, strove to entrap Jesus, that they might accuse him of sedition.
New Catholic Dictionary