a happening | Happening by chance, or unexpectedly; taking place not according to the usual course of things; casual; fortuitous
n (context|painting|pluralonly) 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.
n (context|music) A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.