Lewis & Short

prŏpĭtĭātōrĭus, a, um, adj. [propitiator], atoning, reconciling (eccl. Lat.): bonitas Dei, Ambros. Fug. Sec. 3, 14.
Hence, subst.:prŏpĭtĭātōrĭum, ĭi, n.

  1. I. A means of reconciliation, an atonement, propitiation: propitiatorium, quasi propitiationis oratorium, Isid. Orig. 15, 4; Ambros. Ep. 4, 4.
  2. II. A place of atonement, Vulg. Exod. 25, 17; id. Heb. 9, 5.