The Collaborative International Dictionary of English v.0.48:

Propitiation \Pro*pi`ti*a"tion\, n. [L. propitiatio: cf. F.
   propitiation.]
   [1913 Webster]
   1. The act of appeasing the wrath and conciliating the favor
      of an offended person; the act of making propitious.
      [1913 Webster]

   2. (Theol.) That which propitiates; atonement or atoning
      sacrifice; specifically, the influence or effects of the
      death of Christ in appeasing the divine justice, and
      conciliating the divine favor.
      [1913 Webster]

            He [Jesus Christ] is the propitiation for our sins.
                                                  --1 John ii.
                                                  2.
      [1913 Webster]

WordNet (r) 3.0 (2006):

propitiation
    n 1: the act of placating and overcoming distrust and animosity
         [syn: placation, conciliation, propitiation]
    2: the act of atoning for sin or wrongdoing (especially
       appeasing a deity) [syn: expiation, atonement,
       propitiation]