The Collaborative International Dictionary of English v.0.48:

Palliation \Pal`li*a"tion\, n. [Cf. F. palliation.]
   1. The act of palliating, or state of being palliated;
      extenuation; excuse; as, the palliation of faults,
      offenses, vices.
      [1913 Webster]

   2. Mitigation; alleviation, as of a disease. --Bacon.
      [1913 Webster]

   3. That which cloaks or covers; disguise; also, the state of
      being covered or disguised. [Obs.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

palliation
    n 1: easing the severity of a pain or a disease without removing
         the cause
    2: to act in such a way as to cause an offense to seem less
       serious [syn: extenuation, mitigation, palliation]