The Collaborative International Dictionary of English v.0.48:

Graffito \Graf*fi"to\, n. [It., fr. graffio a scratching.]
   1. (Art) Production of decorative designs by scratching them
      through a surface of layer plaster, glazing, etc.,
      revealing a different-colored ground; also, pottery or
      ware so decorated; -- chiefly used attributively.
      [Webster 1913 Suppl.]

   2. the singular form of graffiti, seldom used.
      [PJC]

WordNet (r) 3.0 (2006):

graffito
    n 1: a rude decoration inscribed on rocks or walls [syn:
         graffito, graffiti]