Wordnet 3.0
ADVERB (1)
1. 
 in an unhappy manner; 
- Example: "he cheerlessly set out to do the task"
The Collaborative International Dictionary of English v.0.48:
Cheerless \Cheer"less\, a.
   Without joy, gladness, or comfort. -- Cheer"less*ly, adv.
   -- Cheer"less*ness, n.
   [1913 Webster]
         My cheerful day is turned to cheerless night.
                                                  --Spenser.
   Syn: Gloomy; sad; comfortless; dispiriting; disconsolate;
        dejected; melancholy; forlorn.
        [1913 Webster]
WordNet (r) 3.0 (2006):
cheerlessly
    adv 1: in an unhappy manner; "he cheerlessly set out to do the
           task" [ant: cheerfully]