Lewis & Short

oppando, pandi, pansum, or passum, 3, v. a. [ob-pando], to spread or stretch out against or before, to spread out (post-class.): aliquid ad flatus helices, Grat. Cyn. 55: cornibus oppansis et summā fronte coruscum (of the cross of Christ), Prud. Psych. 410: aulaei vice oppansā, Tert. Apol. 48 fin.; Hier. Ep. ad Galat. 1, v. 11, 12; Vulg. Exod. 35, 12.
Hence, oppansum (-passum), i, n., a covering, envelope (eccl. Lat.): corporis, Tert. Anim. 53.