birthmark(n = noun.attribute) nevus - a blemish on the skin that is formed before birth;
is a kind of blemish, defect, mar
has particulars: nevus flammeus, port-wine stain, hemangioma simplex, strawberry, strawberry mark

   Some peculiar mark or blemish on the body at birth. [1913 Webster]
"Most part of this noble lineage carried upon their body for a natural birthmark, . . . a snake." [1913 Webster]

birthmark, n. an unusual brown or red mark on one's body at or from birth.

N  blemish, disfigurement, deformity, adactylism, flaw, defect, injury, spots on the sun, eyesore, stain, blot, spot, spottiness, speck, speckle, blur, tarnish, smudge, dirt, freckle, mole, macula, patch, blotch, birthmark, blobber lip, blubber lip, blain, maculation, scar, wem, pustule, whelk, excrescence, pimple, pitted, freckled, discolored, imperfect, blobber-lipped, bloodshot, injured.