The Collaborative International Dictionary of English v.0.48:

Over-arm \O"ver-arm`\, a. (Cricket, etc.)
   Done (as bowling or pitching) with the arm raised above the
   shoulder. See Overhard. "An over-arm with a round-arm
   bowler." --R. A. Proctor.
   [1913 Webster]

WordNet (r) 3.0 (2006):

overarm
    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]