Wordnet 3.0
ADVERB (2)
1. 
 without liveliness; 
- Example: "she nodded her head dully"2. 
 without luster or shine; 
- Example: "the light shone dully through the haze"- Example: "unpolished buttons glinted dully"
The Collaborative International Dictionary of English v.0.48:
Dully \Dul"ly\, adv.
   In a dull manner; stupidly; slowly; sluggishly; without life
   or spirit.
   [1913 Webster]
         Supinely calm and dully innocent.        -- G.
                                                  Lyttelton.
   [1913 Webster]
WordNet (r) 3.0 (2006):
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"