WordNet (r) 3.0 (2006):

unsuitability
    n 1: the quality of having the wrong properties for a specific
         purpose [syn: unsuitability, unsuitableness,
         ineptness] [ant: suitability, suitableness]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "unsuitability":
   Babbittry, aberrance, aberrancy, abnormality, ad lib, anomaly,
   bad taste, bourgeois taste, camp, campiness, criminality,
   delinquency, deviance, deviancy, disqualification, disrepair,
   dissatisfactoriness, extemporaneousness, falling short,
   functionlessness, futility, high camp, illegality, impoliticalness,
   impoliticness, improperness, impropriety, improvisation,
   inadequacy, inadequateness, inadmissibility, inadvisability,
   inapplicability, inappositeness, inappropriateness, inaptitude,
   inaptness, inauspiciousness, incapability, incompetence,
   incongruity, inconvenience, inconveniency, incorrectness,
   indecency, indecorousness, indecorum, indefensibility, indelicacy,
   inelegance, inelegancy, ineptitude, inexpedience, inexpediency,
   infelicity, infraction, inoperability, inoperativeness,
   inopportuneness, inopportunity, insufficiency, insufficientness,
   intempestivity, interruption, intolerability, intrusion, inutility,
   irrelevance, irrelevancy, kitsch, lack of preparation, lateness,
   low camp, maladjustment, mesalliance, misalliance, misjoinder,
   misjoining, mismatch, needlessness, none to spare, nonfulfillment,
   nonpreparation, nonpreparedness, nonsatisfaction, objectionability,
   otiosity, philistinism, planlessness, poor taste, pop, pop culture,
   prematurity, short supply, sinfulness, superfluousness,
   tastelessness, too late, too little, unacceptability,
   unaestheticism, unaestheticness, unbecomingness, uncongeniality,
   undesirability, unemployability, unfavorableness, unfitness,
   unfittedness, unfittingness, unfortunateness, unhelpfulness,
   unlawfulness, unmeetness, unnecessity, unpreparedness,
   unprofitability, unprofitableness, unpropitiousness,
   unqualification, unqualifiedness, unreadiness, unrighteousness,
   unripeness, unsatisfactoriness, unseasonableness, unseemliness,
   unserviceability, unsuitableness, unsuitedness, untenability,
   untimeliness, unusability, unwiseness, uselessness, violation,
   vulgar taste, vulgarism, vulgarity, vulgarness, vulnerability,
   wickedness, worthlessness, wrong, wrongfulness, wrongness