The Collaborative International Dictionary of English v.0.48:

Suitability \Suit`a*bil"i*ty\, n.
   The quality or state of being suitable; suitableness.
   [1913 Webster]

WordNet (r) 3.0 (2006):

suitability
    n 1: the quality of having the properties that are right for a
         specific purpose; "an important requirement is suitability
         for long trips" [syn: suitability, suitableness] [ant:
         ineptness, unsuitability, unsuitableness]

Moby Thesaurus II by Grady Ward, 1.0:

85 Moby Thesaurus words for "suitability":
   ability, acceptability, admissibility, advantage, advantageousness,
   advisability, applicability, appositeness, appropriateness,
   aptitude, aptness, auspiciousness, becomingness, beneficialness,
   capability, chargedness, civility, competence, competency,
   condition, convenience, correctitude, correctness, criticality,
   crucialness, decencies, decency, decorousness, decorum,
   desirability, eligibility, eligible, expedience, expediency,
   favorableness, feasibility, felicitousness, felicity, fitness,
   fittedness, fittingness, fruitfulness, genteelness, gentility,
   goodness, happiness, loadedness, mastery, maturity, meetness,
   niceness, normality, normativeness, opportuneness, percentage,
   politicness, pregnancy, preparedness, proficiency, profit,
   profitability, properness, propitiousness, proprieties, propriety,
   prudence, qualification, readiness, relevance, righteousness,
   rightness, ripeness, seasonableness, seasoning, seemliness,
   suitableness, suitedness, tempering, timeliness, trim, urbanity,
   usefulness, wisdom, worthiness, worthwhileness