WordNet (r) 3.0 (2006):

irrelevance
    n 1: the lack of a relation of something to the matter at hand
         [syn: irrelevance, irrelevancy] [ant: relevance,
         relevancy]

Moby Thesaurus II by Grady Ward, 1.0:

74 Moby Thesaurus words for "irrelevance":
   abnormality, anomaly, disassociation, disconnection, discreteness,
   disjunction, disjuncture, dissociation, immateriality,
   impertinence, impropriety, inadmissibility, inapplicability,
   inappositeness, inappropriateness, inaptitude, inaptness,
   inauspiciousness, inconnection, inconsequence, inconsequentiality,
   inconsiderableness, inconvenience, independence, indifference,
   ineffectuality, inexpedience, infelicity, inferiority,
   inopportuneness, inopportunity, insignificance, intempestivity,
   interruption, intrusion, irrelation, irrelevancy, lateness,
   littleness, low priority, maladjustment, marginality, mesalliance,
   misalliance, misjoinder, misjoining, mismatch, negligibility,
   pettiness, picayune, picayunishness, pokiness, prematurity,
   puniness, secondariness, separateness, slightness, smallness,
   uncongeniality, unconnectedness, unfavorableness, unfitness,
   unfittingness, unfortunateness, unimportance, unimpressiveness,
   unnoteworthiness, unpropitiousness, unrelatedness, unripeness,
   unseasonableness, unsuitability, untimeliness, wrongness