The Collaborative International Dictionary of English v.0.48:

Hearten \Heart"en\ (h[aum]rt"'n), v. t. [From Heart.]
   1. To encourage; to animate; to incite or stimulate the
      courage of; to embolden.
      [1913 Webster]

            Hearten those that fight in your defense. --Shak.
      [1913 Webster]

   2. To restore fertility or strength to, as to land.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hearten
    v 1: give encouragement to [syn: cheer, hearten, recreate,
         embolden] [ant: dishearten, put off]

Moby Thesaurus II by Grady Ward, 1.0:

70 Moby Thesaurus words for "hearten":
   abet, advocate, aid and abet, animate, arouse, assure, bear up,
   bolster, boost, brace up, brighten, buck up, buoy up, cheer,
   chirk up, comfort, condole with, console, countenance, dynamize,
   ease, electrify, embolden, encourage, endorse, energize, enliven,
   exhilarate, favor, fire, galvanize, give a lift, give comfort,
   gladden, go for, inflame, inspire, inspirit, invigorate, jazz up,
   keep in countenance, kindle, liven, nerve, pep up, perk up,
   pick up, put at ease, quicken, rally, reassure, rejoice,
   rejoice the heart, relieve, rouse, set at ease, shine upon,
   smile upon, snap up, solace, steel, stimulate, stir, strengthen,
   subscribe, support, sympathize with, vitalize, warm, zip up