Definitions of accidental:

  • noun:   a musical notation that makes a note sharp or flat or natural although that is not part of the key signature
  • adjective:   without intention (especially resulting from heedless action)
    Example: "Accidental poisoning"
  • adjective:   associated by chance and not an integral part
    Example: "Poetry is something to which words are the accidental, not by any means the essential form- Frederick W. Robertson"
  • adjective:   occurring or appearing or singled out by chance
    Example: "Their accidental meeting led to a renewal of their friendship"