Source : Webster's Revised Unabridged Dictionary (1913)

Thereto \There*to"\, adv.
   1. To that or this. --Chaucer.

   2. Besides; moreover. [Obs.] --Spenser.

            Her mouth full small, and thereto soft and red.
                                                  --Chaucer.

Source : WordNet®

thereto
     adv : to that; "with all the appurtenances fitting thereto" [syn:
           {to it}, {to that}]