The Collaborative International Dictionary of English v.0.48:

Overhand \O"ver*hand`\, n.
   1. The upper hand; advantage; superiority; mastery.
      [1913 Webster]

            He had gotten thereby a great overhand on me. --Sir
                                                  T. More.
      [1913 Webster]

   2. (Baseball) A throwing or pitching style that is
      overhanded; also an overhand[2] pitch.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Overhand \O"ver*hand`\, a.
   1. (Sewing) Over and over; -- applied to a style of sewing,
      or to a seam, in which two edges, usually selvedges, are
      sewed together by passing each stitch over both.
      [1913 Webster]

   2. (Baseball, Cricket, Tennis, etc.) Done (as pitching or
      bowling) with the hand higher than the elbow, or the arm
      above, or higher than, the shoulder; as, an overhand
      pitch; an overhand stroke.
      [1913 Webster +PJC]

   Overhand knot. See Illustration of Knot.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Overhand \O"ver*hand`\, adv.
   In an overhand manner or style.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overhand
    adj 1: with hand brought forward and down from above shoulder
           level; "an overhand pitch"; "an overhand stroke" [syn:
           overhand, overhanded, overarm] [ant: underarm,
           underhand, underhanded]
    2: sewn together with overhand stitches (close vertical stitches
       that pass over and draw the two edges together) [syn:
       overhand, oversewn]