accidental

adj

1. Pertaining to accident and not essence; thus, inessential; incidental; secondary.
2. Pertaining to accident and not essence; thus, inessential; incidental; secondary.
3. Adjusted by one or two semitones, in temporary departure from the key signature.
4. Occurring sometimes, by chance; occasional.
5. Happening by chance, or unexpectedly; taking place not according to the usual course of things; by accident, unintentional.

   “The discovery was purely accidental.”

   “He was killed by an accidental gunshot.”

   “accidental damage”

   “accidental death”

   “entirely accidental”

6. Being a double point with two distinct tangent planes in 4-dimensional projective space.

noun

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

   “He conceived it just that accidentals ... should sink with the substance of the accusation.”

2. (plural, plural-only)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.
3. A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.
4. Part of a text that has a mainly structural purpose, such as spelling, punctuation, or capitalization.