Source : Webster's Revised Unabridged Dictionary (1913)

Heteroousian \Het`er*o*ou`si*an\, a. [Hetero- + Gr. ? being,
   essence.]
   Having different essential qualities; of a different nature.

Heteroousian \Het`er*o*ou"si*an\, n. (Eccl. Hist.)
   One of those Arians who held that the Son was of a different
   substance from the Father.