General:
* Disability
* Impairment
* Disadvantage
* Inability
* Limitation
* Challenge
Referring to a competitive advantage:
* Head start
* Allowance
* Adjustment
* Compensation
Referring to a physical or mental limitation:
* Inability
* Disability
* Impairment
* Weakness
* Defect
Referring to a disadvantage in life:
* Barrier
* Obstacle
* Setback
* Hindrance
The best synonym to use will depend on the specific meaning you are trying to convey. For example, if you are talking about a person's physical limitations, "disability" might be the most appropriate term. If you are talking about a competitive advantage, "head start" might be better.
It's important to be sensitive to the language used when discussing disabilities. Avoid using terms that are considered offensive or derogatory.