accidental

nouns

a musical notation that makes a note sharp or flat or natural although that is not part of the key signature

accidental

is a type of (narrower)

(music) notation used by musicians

happening by chance or unexpectedly or unintentionally

"with an inadvertent gesture she swept the vase off the table"; "accidental poisoning"; "an accidental shooting"

accidental, inadvertent

is derived from