Source : Webster's Revised Unabridged Dictionary (1913)

Dully \Dul"ly\, adv.
   In a dull manner; stupidly; slowly; sluggishly; without life
   or spirit.

         Supinely calm and dully innocent.        -- G.
                                                  Lyttelton.

Source : WordNet®

dully
     adv 1: without liveliness; "she nodded her head dully"
     2: without luster or shine; "the light shone dully through the
        haze"; "unpolished buttons glinted dully"