The Collaborative International Dictionary of English v.0.48:

Orismology \O`ris*mol"o*gy\ ([=o]`r[i^]s*m[o^]l"[-o]*j[y^]), n.
   [Gr. "orismo`s a marking out by boundaries, the definition of
   a word + -logy. See Horizon.]
   That department of natural history which treats of technical
   terms; the science of defining technical terms.
   [1913 Webster]