(derogatory) a person who is a faithful supporter of someone, especially such a person who would be willing to do dishonest things or engage in crime to serve them;
e.g. The mob boss sent his henchman to finish off the enemy.
(noun)
(derogatory) a loyal political supporter of someone, especially one who offers their support with the aim or purpose of seeking personal advantage;
e.g. The politician's henchman does not get punished for committing crimes.
(noun)
a person employed as an attendant to someone high-ranking;
e.g. The lord asked his henchman to show the visitor in.