- The definition of unable is a person or thing that doesn't have the ability, power or authority to do something.
An example of unable is someone not being qualified to fly a plane.
This airplane is unable to fly.
- not able; lacking the ability, means, or power to do something
- helpless; feeble
- Lacking the necessary power, authority, or means; not able; incapable: unable to get to town without a car.
- Lacking mental or physical capability or efficiency; incompetent: unable to walk.
- Usage Problem Not susceptible to action or treatment: a project unable to be financed with government funds. See Usage Note at able.