Henchman often implies negative judgement; used for those helping in wrongdoing. The dictator was often seen surrounded by his henchmen.
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Not Ordinary Staff
Henchman isn't used for regular employees; it's for close, personal followers. The company CEO would never call his executive assistant a henchman.
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Fictional Use
In movies and books, 'henchman' describes villains' loyal supporters, often involved in action. The superhero battled the villain's henchmen before confronting him.