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1. Far beyond what is usual in magnitude or degree
   "an exceptional memory";
   - exceeding, olympian, prodigious, surpassing
    
2. Surpassing what is common, usual or expected
   "exceptional kindness";
   - especial, particular, special
    
3. (psychology) deviating widely from a norm of physical or mental ability; used especially of children below normal in intelligence
   "special educational provisions for exceptional children"

See also: abnormal, extraordinary, uncommon

Encyclopedia: Exceptional