plural of ability

(obsolete) Suitableness. / (uncountable) The quality or state of being able; capacity to do or of doing something; having the necessary power. / The legal wherewithal to act.

Forms a noun from a verb or an adjective by changing from -able; ability, inclination or suitability for a specified function or condition.

plural of ability to pay

(taxation) An individual's level of wealth or income, as a measure of the tax rate they can afford to pay.

The practice of putting students together in groups of those with similar skills or needs, e.g. in classes or in groups within a class.