Source : Webster's Revised Unabridged Dictionary (1913)

Assuasive \As*sua"sive\, a. [From assuage, as if this were fr. a
   supposed L. assuadere to persuade to; or from E. pref. ad +
   -suasive as in persuasive.]
   Mitigating; tranquilizing; soothing. [R.]

         Music her soft assuasive voice applies.  --Pope.

Source : WordNet®

assuasive
     adj : freeing from fear and anxiety [syn: {calming}, {pacifying},
           {soothing}]