The Collaborative International Dictionary of English v.0.48:

Suitable \Suit"a*ble\, a.
   Capable of suiting; fitting; accordant; proper; becoming;
   agreeable; adapted; as, ornaments suitable to one's station;
   language suitable for the subject. -- Suit"a*ble*ness, n.
   -- Suit"a*bly, adv.
   [1913 Webster]

   Syn: Proper; fitting; becoming; accordant; agreeable;
        competent; correspondent; compatible; consonant;
        congruous; consistent.
        [1913 Webster]

WordNet (r) 3.0 (2006):

suitableness
    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]