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.