Source : Webster's Revised Unabridged Dictionary (1913)

Birthmark \Birth"mark`\, n.
   Some peculiar mark or blemish on the body at birth.

         Most part of this noble lineage carried upon their body
         for a natural birthmark, . . . a snake.  --Sir T.
                                                  North.

Source : WordNet®

birthmark
     n : a blemish on the skin formed before birth [syn: {nevus}]