The Collaborative International Dictionary of English v.0.48:

Stelography \Ste*log"ra*phy\, n. [Gr. ? a post, slab, pillar +
   -graphy: cf. Gr. ? an inscription on a tablet.]
   The art of writing or inscribing characters on pillars. [R.]
   --Stackhouse.
   [1913 Webster] Stem