stupidity

a poor ability to understand or to profit from experience

• denseness, dumbness, slow-wittedness — the quality of being mentally slow and limited
• dullness, dulness, obtuseness — the quality of being slow to understand
• retardation, mental retardation, backwardness, slowness, subnormality — lack of normal development of intellectual capacities
• folly, foolishness, craziness — the quality of being rash and foolish

• inability — lack of ability (especially mental ability) to do something