Source : Webster's Revised Unabridged Dictionary (1913)

Aga \A*ga"\ or Agha \A*gha"\, n. [Turk. adh[=a] a great lord,
   chief master.]
   In Turkey, a commander or chief officer. It is used also as a
   title of respect.

Source : WordNet®

Aga
     n : title for a civil or military leader (especially in Turkey)
         [syn: {Agha}]