The word ‘ability’ refers to the power, skill, or talent to do something successfully. It indicates a person’s competence or capability to perform a task effectively.
For example:
• She has the ability to solve difficult mathematical problems.
• His ability to speak multiple languages is impressive.
The opposite of this concept is the lack of such power, skill, or capacity — the state of being unable to do something. This opposite idea is expressed by the word ‘inability’.
For example:
• His inability to concentrate caused him to fail the exam.
• The inability to make quick decisions can lead to poor results.
Thus, the antonym of ‘ability’ is ‘inability’ as it denotes the absence of capability or competence.