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

(painting, 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.

(music) A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.

Part of a text that has a mainly structural purpose, such as spelling, punctuation, or capitalization.

An adjective "accidental" refers to something that is not essential or inherent, but rather incidental or secondary, particularly in aristotelian philosophy.

(music) Adjusted by one or two semitones, in temporary departure from the key signature.

Occurring sometimes, by chance; occasional.

Happening by chance, or unexpectedly; taking place not according to the usual course of things; by accident, unintentional.

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