The Collaborative International Dictionary of English v.0.48:

Inobservance \In`ob*serv"ance\, a. [L. inobservantia : cf. F.
   inobservance.]
   Lack or neglect of observance. --Bacon.
   [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

52 Moby Thesaurus words for "inobservance":
   absentmindedness, carelessness, default, delinquency, dereliction,
   disconformity, disregard, disregardfulness, distraction, failure,
   flightiness, flippancy, frivolousness, giddiness, heedlessness,
   inadvertence, inadvertency, inattention, inattentiveness,
   inconsideration, incuriosity, indifference, laxity, levity,
   lightmindedness, neglect, negligence, nonadherence, noncompliance,
   nonconformance, nonconformity, nonfeasance, nonfulfillment,
   nonobservance, nonperformance, obliviousness, omission, oversight,
   regardlessness, shallowness, slight, superficiality,
   thoughtlessness, unalertness, unawareness, unconsciousness,
   unheedfulness, unintentiveness, unmindfulness, unobservance,
   unwariness, unwatchfulness