WordNet (r) 3.0 (2006):

reassuring
    adj 1: restoring confidence and relieving anxiety; "a very
           reassuring remark" [ant: unreassuring, worrisome]

Moby Thesaurus II by Grady Ward, 1.0:

26 Moby Thesaurus words for "reassuring":
   assuring, auspicious, bright with promise, cheering, comforting,
   condolatory, condolent, condoling, consolatory, consoling,
   encouraging, favorable, full of promise, heartening, hospitable,
   inspiring, inspiriting, looking up, of good comfort, of promise,
   pregnant of good, promising, propitious, relieving, supportive,
   sympathetic