Source : Webster's Revised Unabridged Dictionary (1913)

Breast-deep \Breast"-deep`\ (br[e^]st"d[=e]p`), a.
   Deep as from the breast to the feet; as high as the breast.

         Set him breast-deep in earth, and famish him. --Shak.

Source : WordNet®

breast-deep
     adv : up to the breast; "we were standing breast-high in the
           water" [syn: {breast-high}]