accidental

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.

Part of a text that has a mainly structural purpose, such as spelling, punctuation or capitalization.