Correct spelling for the English word "stenion" is [stˈɛni͡ən], [stˈɛniən], [s_t_ˈɛ_n_iə_n] (IPA phonetic alphabet).
The termination in either temporal fossa of the shortest transverse diameter of the skull, a craniometric point.
A practical medical dictionary. By Stedman, Thomas Lathrop. Published 1920.