accidental

adjective

• 1happening by chance, unintentionally, or unexpectedly:a verdict of accidental death the damage might have been accidental

• 2incidental; subsidiary:the location is accidental and contributes nothing to the poem

• 3 Philosophy (in Aristotelian thought) relating to or denoting properties which are not essential to a thing’s nature.

noun

• 1 Music a sign indicating a momentary departure from the key signature by raising or lowering a note: horn parts are usually written without key signature, the necessary accidentals being added

• 2 Ornithologyanother term for vagrant.