The Collaborative International Dictionary of English v.0.48:

Laxness \Lax"ness\, n.
   The state of being lax; laxity.
   [1913 Webster]

WordNet (r) 3.0 (2006):

laxness
    n 1: the quality of being lax and neglectful [syn: laxness,
         laxity, remissness, slackness]
    2: the condition of being physiologically lax; "baths can help
       the laxness of the bowels" [syn: laxness, laxity]

Moby Thesaurus II by Grady Ward, 1.0:

97 Moby Thesaurus words for "laxness":
   Fabian policy, Micawberism, abandon, abandonment, acceptance,
   backwardness, bagginess, clemency, clementness, compassion, culpa,
   culpable negligence, default, dereliction, dilatoriness, disregard,
   easiness, easygoingness, failure, flabbiness, flaccidity,
   flaccidness, floppiness, forbearance, forbearing, gentleness,
   hesitation, hold-off, humaneness, humanity, immoderacy,
   inadvertence, inadvertency, inattention, incontinence,
   indiscipline, intemperance, irrepressibility, laches,
   laissez-faire, lapse, laxation, laxity, lenience, leniency,
   lenientness, lenity, licentiousness, limpness, looseness,
   mercifulness, mercy, mildness, moderateness, mugwump, neglect,
   neglectfulness, negligence, noncoercion, nonfeasance,
   noninterference, nonintimidation, nonperformance, nonrestriction,
   omission, overlooking, oversight, patience, permissiveness, pity,
   poor stewardship, procrastination, relaxation, remissness,
   ricketiness, riotousness, rubberiness, shakiness, slackness,
   slight, sloppiness, slowness, softness, stall, temporization,
   tenderness, tolerance, unconstraint, uncontrol, uninhibitedness,
   unreserve, unrestraint, unrigorousness, unruliness, unstrictness,
   wantonness, wildness