The Collaborative International Dictionary of English v.0.48:

Listless \List"less\, a. [OE. listles, lustles. See Lust.]
   Having no desire or inclination; indifferent; heedless;
   spiritless. " A listless unconcern." --Thomson.
   [1913 Webster]

         Benumbed with cold, and listless of their gain.
                                                  --Dryden.
   [1913 Webster]

         I was listless, and desponding.          --Swift.

   Syn: Heedless; careless; indifferent; vacant; uninterested;
        languid; spiritless; supine; indolent. --
        List"less*ly, adv. -- List"less*ness, n.
        [1913 Webster]

WordNet (r) 3.0 (2006):

listlessness
    n 1: a feeling of lack of interest or energy [syn: languor,
         lassitude, listlessness]
    2: inactivity resulting from lethargy and lack of vigor or
       energy [syn: listlessness, torpidity, torpidness,
       torpor]