The Collaborative International Dictionary of English v.0.48:

Loathsome \Loath"some\, a.
   Fitted to cause loathing; exciting disgust; disgusting; as, a
   loathsome disease.
   [1913 Webster]

         The most loathsome and deadly forms of infection.
                                                  --Macaulay.
   -- Loath"some*ly. adv. -- Loath"some*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

loathsomeness
    n 1: the quality of being disgusting to the senses or emotions;
         "the vileness of his language surprised us" [syn:
         loathsomeness, repulsiveness, sliminess, vileness,
         lousiness, wickedness]