Definition of accidental

• a musical notation that makes a note sharp or flat or natural although that is not part of the key signature
• associated by chance and not an integral part; "poetry is something to which words are the accidental, not by any means the essential form"- Frederick W. Robertson; "they had to decide whether his misconduct was adventitious or the result of a flaw in his character"
• occurring or appearing or singled out by chance; "their accidental meeting led to a renewal of their friendship"; "seek help from casual passers-by"; "a casual meeting"; "a chance occurrence"