1. adjective
a) Happening by chance, or unexpectedly; taking place not according to the usual course of things; casual; fortuitous
an accidental visit
b) Nonessential; not necessary belonging; incidental
are accidental to a play
2. noun
b) 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.
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