Source : Webster's Revised Unabridged Dictionary (1913)

Merlon \Mer"lon\, n. [F., perh. fr. L. moerus, for murus a wall,
   through (assumed) dim. moerulus.] (Fort.)
   One of the solid parts of a battlemented parapet; a
   battlement. See Illust. of {Battlement}.

Source : WordNet®

merlon
     n : a solid section between two crenels in a crenelated
         battlement