n 1  :  an unfortunate event resulting from carelessness, unawareness, ignorance, or a combination of causes  2  :  an unexpected bodily event of medical importance esp. when injurious <the paralytic occurred between the 8th and 21st day after the initial injection -Jour. Amer. Med. Assoc.>  <a cerebral vascular >   3  :  an unexpected happening causing loss or injury which is not due to any fault or misconduct on the part of the person injured but for which legal relief may be sought ac*ci*den*tal adj ac*ci*den*tal*ly also  ac*ci*dent*ly  adv 
 
    
 
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