Holman Bible Dictionary 
Matthew 22:15-22 Mark 12:13-17 Mark 3:6Herod
Webster's Dictionary 
(n.) One of a party among the Jews, composed of partisans of Herod of Galilee. They joined with the Pharisees against Christ.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
(only in the plur. ῾Ηρωδιανοί ), the designation of a class of Jews that existed in the time of Jesus Christ, evidently, as the name imports, partisans of Herod, but whether of a political or religious description it is not easy, for want of materials, to determine. The passages of the New Testament which refer to them are the following: Mark 3:6; Mark 12:13; Matthew 22:16; Luke 20:20. From these it appears that the ecclesiastical authorities of Judaea held a council against our Savior, and, associating with themselves the Herodians, sent an embassy to him with the express but covert design of ensnaring him in his speech, that thus they might compass his destruction, by embroiling him. But what additional difficulty did the Herodians bring? Herod Antipas was now tetrarch of Galilee and Persea, which was the only inheritance he received from his father, Herod the Great. As tetrarch of Galilee he was specially the ruler of Jesus, whose home was in that province. The Herodians, then, may have been subjects of Herod, Galilueans, whose evidence the priests were desirous of procuring, because theirs would be the evidence of fellow-countrymen, and of special force with Antipas as being that of his own immediate subjects ( Luke 23:7). Herod's relations with Rome were in an unsafe condition. He was a weak prince, given to ease and luxury, and his wife's ambition conspired with his own desires to make him strive to obtain from the emperor Caligula the title of king. For this purpose he took a journey to Rome, but he was banished to Lyons, in Gaul. The Herodians may have been favorers of his pretensions; if so, they would be partial hearers, and eager witnesses against Jesus before the Roman tribunal. It would be a great service-to the Romans to be the means of enabling them to get rid of one who aspired to be king of the Jews.
It would equally gratify their own lord should the Herodians give effectual aid in putting a period, to the mysterious yet formidable claims of a rival claimant of the crown. If the Herodians were a Galilaean political party who were eager to procure from Rome the honor of royalty for Herod ( Mark 6:14, the name of king is merely as of courtesy), they were chosen as associates by the Sanhedrim with especial propriety. This idea is confirmed by Josephus's mention of a party as "the partisans of Herod" ( Οἱ Τὰ ῾Ηρώδου Φανοῦντες Ant. 14, 15, 10). The deputation were to "feign themselves just men," that is, men whose sympathies were entirely Jewish, and, as such, anti-heathen: they were to intimate their dislike of paying tribute, as being an acknowledgment of a foreign yoke; and by flattering Jesus, as one who loved truth, feared no man, and would say what he thought, they meant to inveigle him into a condemnation of the practice. In order to carry these base and hypocritical designs into effect, the Herodians were appropriately associated with the Pharisees; for as the latter were the recognized conservators of Judaism, so the former were friends of the aggrandizement of a native as against a foreign prince. (Comp. Fritzsche and Walch, ad loc. Other hypotheses may be found in Paulus on the passage in Matt.; in Wolff, Curae Phil. 1, 311 sq.; see also Kecher, Analect. in loc. Matt.; Zorn, Hist. fisci. Juzd. p. 127; Otho, Lex. Rabb. p. 275. Monographs on this subject are those of Steuch, Diss. de Herod. Lund. 1706; Floder, Diss. de Herod. Upsal, 1764; Schmid, Epist. de Herod. Lipsise, 1763; Leuschner, De Secta Herodianor. Hirschberg, 1751; Stollberg, De Haerodianis, Viteb. 1666; Jensius, id. Jen. 1688.) (See Jewish Sects).