1. suffering from dementia or severe mental illness
Usage: medical
2. extremely foolish or irrational
Usage: informal

Examples

• The demented patient required constant supervision.
• His demented behavior worried his family.
• She thought his plan was completely demented.
• The demented scheme was doomed to fail.
• Only someone demented would attempt such a dangerous stunt.
• The elderly man’s demented state made communication difficult.