Source : Webster's Revised Unabridged Dictionary (1913)

Deferentially \Def`er*en"tial*ly\, adv.
   With deference.

Source : WordNet®

deferentially
     adv 1: in a servile manner; "he always acts so deferentially around
            his superviser" [syn: {submissively}]
     2: in a respectfully deferential manner; "he listened
        deferentially"