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]

WordNet (r) 3.0 (2006):

right-hand
    adj 1: located on or directed toward the right; "a right-hand
           turn"
    2: intended for the right hand; "a right-hand glove" [syn:
       right(a), right-hand(a)]
    3: most helpful and reliable; "my right-hand man"