Source : Webster's Revised Unabridged Dictionary (1913)

Chicken-breasted \Chick"en-breast`ed\, a.
   Having a narrow, projecting chest, caused by forward
   curvature of the vertebral column.

Source : WordNet®

chicken-breasted
     adj : having a chest deformity marked by a projecting breastbone
           caused by infantile rickets [syn: {pigeon-breasted}]