noun

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

2. 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.

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

adjective

1. Not essential; incidental, secondary.

2. Nonessential to something's inherent nature (especially in Aristotelian thought).

3. Adjusted by one or two semitones, in temporary departure from the key signature.

Synonyms: adventitious, casual, contingent, fortuitous, incidental, occasional, serendipitous, circumstantial