The Collaborative International Dictionary of English v.0.48:

Lonesome \Lone"some\, a. [Compar. Lonesomer; superl.
   Lonesomest.]
   1. Secluded from society; not frequented by human beings;
      solitary.
      [1913 Webster]

            Like one that on a lonesome road
            Doth walk in fear and dread.          --Coleridge.
      [1913 Webster]

   2. Conscious of, and somewhat depressed by, solitude; as, to
      feel lonesome.
      [1913 Webster] -- Lone"some*ly, adv. --
      Lone"some*ness, n.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

lonesomeness \lone"some*ness\ n.
   1. a disposition toward being alone.

   Syn: aloneness, loneliness, solitude.
        [WordNet 1.5]

   2. The condition of being alone; the feeling of sadness
      resulting from being alone.
      [PJC]

WordNet (r) 3.0 (2006):

lonesomeness
    n 1: a disposition toward being alone [syn: aloneness,
         loneliness, lonesomeness, solitariness]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "lonesomeness":
   alienation, aloneness, aloofness, celibacy, detachment, isolation,
   keeping apart, loneliness, loneness, moving apart, privacy,
   seclusion, separateness, sequestration, single blessedness,
   singleness, solitariness, solitude, splendid isolation,
   withdrawal