Source : Webster's Revised Unabridged Dictionary (1913)

Monolith \Mon"o*lith\, n. [F. monolithe, L. monolithus
   consisting of a single stone, Gr. ?; ? single + ? stone.]
   A single stone, especially one of large size, shaped into a
   pillar, statue, or monument.

Source : WordNet®

monolith
     n : a single great stone (often in the form of a column or
         obelisk)