Ability, n.; pl. Abilities(#).
Etymology: [F. habileté, earlier spelling habilité (with silent h), L. habilitas aptitude, ability, fr. habilis apt. See Able.]
The quality or state of being able; power to perform, whether physical, moral, intellectual, conventional, or legal; capacity; skill or competence in doing; sufficiency of strength, skill, resources, etc.; -- in the plural, faculty, talent. Then the disciples, every man according to his ability, determined to send relief unto the brethren. Acts xi. 29. Natural abilities are like natural plants, that need pruning by study. Bacon. The public men of England, with much of a peculiar kind of ability. Macaulay.
Syn. -- Capacity; talent; cleverness; faculty; capability; efficiency; aptitude; aptness; address; dexterity; skill. Ability, Capacity. These words come into comparison when applied to the higher intellectual powers. Ability has reference to the active exercise of our faculties. It implies not only native vigor of mind, but that ease and promptitude of execution which arise from mental training. Thus, we speak of the ability with which a book is written, an argument maintained, a negotiation carried on, etc. It always something to be done, and the power of doing it. Capacity has reference to the receptive powers. In its higher exercises it supposes great quickness of apprehension and breadth of intellect, with an uncommon aptitude for acquiring and retaining knowledge. Hence it carries with it the idea of resources and undeveloped power. Thus we speak of the extraordinary capacity of such men as Lord Bacon, Blaise Pascal, and Edmund Burke. "Capacity," says H. Taylor, "is requisite to devise, and ability to execute, a great enterprise." The word abilities, in the plural, embraces both these qualities, and denotes high mental endowments.
Shades of meaning
Fernald has no entry of its own for ability; he lists it under power.
Where he writes about it:
Ability is nearly coextensive with power, but does not reach the positiveness and vigor that may be included in the meaning of power, ability often implying latent, as distinguished from active power; we speak of an exertion of power, but not of an exertion of ability. — from power
Power and ability include capacity, which is power to receive; but ability is often distinguished from capacity, as power that may be manifested in doing, as capacity is in receiving; one may have great capacity for acquiring knowledge, and yet not possess ability to teach. — from power
Faculty is an inherent quality of mind or body; talent, some special mental ability. — from power