Invalid (adjective)

1. Not legally or medically recognized or effective.
2. Not logically or demonstrably true or valid.
3. Lacking in strength, force, or effectiveness.

Origin:

Late latin invalidus 'not strong,' from in- 'not' + validus 'strong, powerful'.

Examples:

1. The contract was declared invalid because it violated the law.
2. The argument was invalid because it was based on false premises.
3. The invalid was confined to a wheelchair for the rest of his life.
4. The statement was invalidated by the evidence presented in court.
5. The invalid vote was not counted in the final tally.