Source : Webster's Revised Unabridged Dictionary (1913)

Mournful \Mourn"ful\, a.
   Full of sorrow; expressing, or intended to express, sorrow;
   mourning; grieving; sad; also, causing sorrow; saddening;
   grievous; as, a mournful person; mournful looks, tones, loss.
   -- {Mourn"ful*ly}, adv. -- {Mourn"ful*ness}, n.

   Syn: Sorrowful; lugubrious; sad; doleful; heavy; afflictive;
        grievous; calamitous.

Source : WordNet®

mournfully
     adv : in a mournful manner; "the young man stared into his glass
           mournfully"