(n.) The quality of being imbecile; weakness; feebleness, esp. of mind.

amentia arrested development asininity backwardness battiness blithering idiocy brainlessness buffoonery clownishness crackpottedness crankiness craziness cretinism daffiness desipience disability disablement disqualification eccentricity fatuity fatuousness folly foolery foolheadedness foolishness frivolity frivolousness giddiness goofiness half-wittedness idiocy idiotism inability inadequacy inanity incapability incapacitation incapacity incompetence incompetency inefficiency ineptitude infancy infantilism inferiority insanity insufficiency legal incapacity lunacy madness mental defectiveness mental deficiency mental handicap mental retardation mindlessness minority mongolianism mongolism mongoloid idiocy moronism moronity niaiserie nugacity nuttiness profound idiocy queerness retardation retardment sappiness screwiness senselessness silliness simple-wittedness simplemindedness simpleness simplicity stupidity subnormality thoughtlessness triflingness triviality unfitness wackiness wardship weirdness witlessness zaniness zanyism