Accidental

Happening by chance, or unexpectedly; taking place not according to the usual course of things; casual; fortuitous; as, an accidental visit.

Nonessential; not necessary belonging; incidental; as, are accidental to a play.

A property which is not essential; a nonessential; anything happening accidentally.

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.

A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.