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.
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.