The Oxford Thesaurus An A-Z Dictionary of Synonyms - aptituden.

1) fitness, suitability, appropriateness, relevance, applicability, suitableness, aptness: One need only look at an albatross in the air to appreciate its aptitude for flight. 2) tendency, propensity, disposition, predilection, bent, proclivity; talent, gift, ability, capability, facility, faculty, flair: Helen displays a natural aptitude for the violin. 3) intelligence, quick-wittedness, intellect; capacity, aptness: The aptitude of that new student sets her apart from the others in the class.