The Collaborative International Dictionary of English v.0.48:

Dehort \De*hort"\, v. t. [imp. & p. p. Dehorted; p. pr. & vb.
   n. Dehorting.] [L. dehortari; de- + hortari to urge,
   exhort.]
   To urge to abstain or refrain; to dissuade. [Obs.]
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         The apostles vehemently dehort us from unbelief. --Bp.
                                                  Ward.
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         "Exhort" remains, but dehort, a word whose place
         neither "dissuade" nor any other exactly supplies, has
         escaped us.                              --Trench.
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