Meaning of ACCIDENTAL in English

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

2. accidental ·noun a property which is not essential; a nonessential; anything happening accidentally.

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

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

5. accidental ·noun 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.

Webster English vocab.      Английский словарь Webster.