the quality of being able to perform; a quality that permits or facilitates achievement or accomplishment
"Her ability to solve complex problems quickly impressed everyone on the team."
Suitableness.
"This new software update demonstrates a surprising ability to run smoothly on older hardware models."
In plain English: Ability is the power or skill you have to do something.
"She showed great ability to solve the complex puzzle quickly."
Usage: Use "ability" to describe the capacity or skill to perform a specific task, not the general quality of being suitable for a situation. For example, say she has the ability to solve complex problems rather than that her ability makes her suitable for the job.
First attested in the 1300s, the word "ability" entered English via Middle English and Old French from Latin habilitās. The original Latin root meant "aptness" or being "fit," which evolved into our modern sense of skill or capacity.