The Collaborative International Dictionary of English v.0.48:

Idleness \I"dle*ness\, n. [AS. [imac]delnes.]
   The condition or quality of being idle (in the various senses
   of that word); uselessness; fruitlessness; triviality;
   inactivity; laziness.

   Syn: Inaction; indolence; sluggishness; sloth.
        [1913 Webster]

WordNet (r) 3.0 (2006):

idleness
    n 1: having no employment [syn: idleness, idling, loafing]
    2: the quality of lacking substance or value; "the
       groundlessness of their report was quickly recognized" [syn:
       groundlessness, idleness]
    3: the trait of being idle out of a reluctance to work [syn:
       faineance, idleness]

The Devil's Dictionary (1881-1906):

IDLENESS, n.  A model farm where the devil experiments with seeds of
new sins and promotes the growth of staple vices.