Entry 2 senses · 2 variants Webster, 1913 Heteroousian · Het·er·o·ou·si·an · IPA /hɛtəɹəʊˈuːzɪən/ a. n. 01 a. Having different essential qualities; of a different nature. 1. Having different essential qualities; of a different nature. 02 n. One of those Arians who held that the Son was of a different substance from the Father. 1. One of those Arians who held that the Son was of a different substance from the Father.(Eccl. Hist.)