Correct spelling for the English word "masrium" is [mˈasɹi͡əm], [mˈasɹiəm], [m_ˈa_s_ɹ_iə_m] (IPA phonetic alphabet).
An assumed new element, the existence of which is doubtful.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.