Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
* postscaenĭum or poscaenĭum (-cen-), ii, n. [post-scena], the part of the theatre behind the scenes, the postscenium; trop., for secret, mystery: postscenia vitae, those parts of life which are behind the scenes, Lucr. 4, 1186; v. Lachm. ad h. l.