The Collaborative International Dictionary of English v.0.48:

Contemper \Con*tem"per\ (k[o^]n*t[e^]m"p[~e]r), v. t. [L.
   contemperare, -temperatum; con- + temperare to temper. Cf.
   Contemperate.]
   To modify or temper; to allay; to qualify; to moderate; to
   soften. [Obs.]
   [1913 Webster]

         The antidotes . . . have allayed its bitterness and
         contempered its malignancy.              --Johnson.
   [1913 Webster]