Source : Webster's Revised Unabridged Dictionary (1913)

Steadfastly \Stead"fast*ly\, adv.
   In a steadfast manner; firmly.

         Steadfast believe that whatever God has revealed is
         infallibly true.                         --Wake.

Source : WordNet®

steadfastly
     adv : with resolute determination; "we firmly believed it"; "you
           must stand firm" [syn: {firm}, {firmly}, {unwaveringly}]