Source : Webster's Revised Unabridged Dictionary (1913)

Pigeon-breasted \Pi"geon-breast`ed\, a.
   Having a breast like a pigeon, -- the sternum being so
   prominent as to constitute a deformity; chicken-breasted.

Source : WordNet®

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