Source : Webster's Revised Unabridged Dictionary (1913)

Henchman \Hench"man\, n.; pl. {-men}. [OE. hencheman, henxman;
   prob. fr. OE. & AS. hengest horse + E. man, and meaning, a
   groom. AS. hengest is akin to D. & G. hengst stallion, OHG.
   hengist horse, gelding.]
   An attendant; a servant; a follower. Now chiefly used as a
   political cant term.

Source : WordNet®

henchman
     n : someone who assists in a plot [syn: {confederate}, {collaborator},
          {partner in crime}]