1. severe intellectual disability or mental weakness; lack of intelligence or sound judgment
Usage: formal or medical; now often considered outdated or offensive in clinical contexts; 'intellectual disability' is preferred in modern usage
2. an instance or example of foolish or senseless behavior or thinking
Usage: often used in the plural

Examples

• The doctor's diagnosis of imbecility was based on standardized intelligence tests.
• It would be imbecility to ignore such clear warning signs.
• The plan was riddled with imbecilities that made it unworkable.
• His imbecility in handling the crisis disappointed everyone.
• She could not tolerate the imbecility of his repeated excuses.
• The proposal was full of such obvious imbecilities that it was rejected immediately.