The Collaborative International Dictionary of English v.0.48:

Lugubrious \Lu*gu"bri*ous\, a. [L. lugubris, fr. lugere to
   mourn; cf. Gr. lygro`s sad, Skr. ruj to break.]
   Mournful; indicating sorrow, often ridiculously or feignedly;
   doleful; woful; pitiable; as, a whining tone and a lugubrious
   look.
   [1913 Webster]

         Crossbones, scythes, hourglasses, and other lugubrious
         emblems of mortality.                    --Hawthorne.
   -- Lu*gu"bri*ous*ly, adv. -- Lu*gu"bri*ous*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lugubrious
    adj 1: excessively mournful