Splett, Jochen. "O" Deutsches Wortfamilienwörterbuch. Berlin, Boston: Walter de Gruyter, 2009. 4793-4903. Web. Retrieved 22 May. 2013, from http://www.degruyter.com/view/books/9783110217469/9783110217469.4793/9783110217469.4793.xml

Splett, J. (2009). O. Deutsches Wortfamilienwörterbuch (pp. 4793-4903). Berlin, Boston: Walter de Gruyter. Retrieved 22 May. 2013, from http://www.degruyter.com/view/books/9783110217469/9783110217469.4793/9783110217469.4793.xml

Splett, Jochen. 2009. O. In Deutsches Wortfamilienwörterbuch, 4793-4903. Berlin, Boston: Walter de Gruyter. Retrieved 22 May. 2013, from http://www.degruyter.com/view/books/9783110217469/9783110217469.4793/9783110217469.4793.xml