accidental > define

noun

• A musical notation that makes a note sharp or flat or natural although that is not part of the key signature.

adjective

• Happening by chance or unexpectedly or unintentionally .
  • usage: "with an inadvertent gesture she swept the vase off the table"; "accidental poisoning"; "an accidental shooting"
  • synonyms: inadvertent

• (a.) Happening by chance or unexpectedly; taking place not according to the usual course of things; casual; fortuitous; as, an accidental visit.
• (a.) Nonessential; not necessary belonging; incidental; as, are accidental to a play.
• (n.) A property which is not essential; a nonessential; anything happening accidentally.
• (n.) Those fortuitous effects produced by luminous rays falling on certain objects so that some parts stand forth in abnormal brightness and other parts are cast into a deep shadow.
• (n.) A sharp, flat or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.