Source : Webster's Revised Unabridged Dictionary (1913)

Parnassus \Par*nas"sus\, n. [L., fr. Gr. ?.] (Anc. Geog. & Gr.
   Myth.)
   A mountain in Greece, sacred to Apollo and the Muses, and
   famous for a temple of Apollo and for the Castalian spring.

   {Grass of Parnassus}. (Bot.) See under {Grass}, and
      {Parnassia}.

   {To climb Parnassus}, to write poetry. [Colloq.]