Dwarven, Deep - Duergarim

Duergarim is the most distant relative of the three families of Arenundim, barely resembling either Dusterdorim or Tuzutainim in its spoken form. After several millennia spent in the Underdark, Deep Dwarven has more shared elements with Drow and Undercommon than its Dwarven cousins. 
Due to the highly secretive and inaccessible nature of Deep Dwarven society, not much is understood of Duergarim except that it uses a hybrid of Undermarks and Koraxicon which is fully illegible to non-Duergarin.