Middle English hengestman groom, from Old English hengest stallion + man¹. About 200 years after its original senses ‘groom’ or ‘squire’ had fallen out of use, henchman was reintroduced by Sir Walter Scott in the early 19th cent. to mean the principal attendant of a Highland chief. As its meaning broadened to refer to a follower of any important person, so it quickly acquired derogatory suggestions of an obsequious or self-serving follower. Its frequent connotations of thuggery and gangsterism in current use perhaps come from association with hatchet man