The Collaborative International Dictionary of English v.0.48:

Reassure \Re`as*sure"\ (r[=e]`[.a]*sh[udd]r"), v. t.
   1. To assure anew; to restore confidence to; to free from
      fear or terror.
      [1913 Webster]

            They rose with fear, . . .
            Till dauntless Pallas reassured the rest. --Dryden.
      [1913 Webster]

   2. To reinsure.
      [1913 Webster]

WordNet (r) 3.0 (2006):

reassure
    v 1: cause to feel sure; give reassurance to; "The airline tried
         to reassure the customers that the planes were safe" [syn:
         reassure, assure] [ant: vex, worry]
    2: give or restore confidence in; cause to feel sure or certain;
       "I reassured him that we were safe"

Moby Thesaurus II by Grady Ward, 1.0:

65 Moby Thesaurus words for "reassure":
   afford hope, ascertain, assure, augur well, bear up, bid fair,
   bolster, brace, brace up, buck up, buoy up, certify, cheer, cinch,
   clear up, clinch, comfort, condole with, console, decide,
   determine, dismiss all doubt, ease, embolden, encourage, ensure,
   establish, find out, fix, get at, give comfort, give hope,
   have good prospects, hearten, hold out hope, hold out promise,
   inspire, inspire hope, inspirit, insure, justify hope,
   make certain, make fair promise, make no doubt, make no mistake,
   make sure, make sure of, nail down, nerve, promise, put at ease,
   raise expectations, raise hope, relieve, remove all doubt,
   see that, see to it, set at ease, set at rest, settle, solace,
   sort out, support, sympathize with, uplift