The Collaborative International Dictionary of English v.0.48:

Right-hand \Right"-hand`\, a.
   1. Situated or being on the right; nearer the right hand than
      the left; as, the right-hand side, room, or road.
      [1913 Webster]

   2. Chiefly relied on; almost indispensable.
      [1913 Webster]

            Mr. Alexander Truncheon, who is their right-hand man
            in the troop.                         --Addison.
      [1913 Webster]

   Right-hand rope, a rope which is laid up and twisted with
      the sun, that is, in the same direction as plain-laid
      rope. See Illust. of Cordage.
      [1913 Webster]