Source : Webster's Revised Unabridged Dictionary (1913)

Octoroon \Oc`to*roon"\, n. [L. octo eight + -roon, as in
   quadroon.]
   The offspring of a quadroon and a white person; a mestee.

Source : WordNet®

Octoroon
     n : an offspring of a Quadroon and a White parent; a person who
         is one-eighth Black