Etymology
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-ability 
word-forming element expressing ability, fitness, or capacity, from Latin -abilitas, forming nouns from adjectives ending in -abilis (see -able). Not etymologically related to ability, though popularly connected with it.
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-ile 
also -il, word-forming element denoting ability or capacity, from Old French -il or directly from Latin adjectival suffix -ilis. Used in classical and Medieval Latin to form ordinal numbers, which accounts for its use from late 19c. in statistics (percentile, etc.).
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