- Occurring sometimes, by chance; occasional. [from 16th c.]
- (music) Adjusted by one or two semitones, in temporary departure from the key signature. [from 16th c.]
- (geometry) Being a double point with two distinct tangent planes in 4-dimensional projective space.
- (philosophy) Nonessential to something's inherent nature (especially in Aristotelian thought). [from 14th c.]
- Happening by chance, or unexpectedly; taking place not according to the usual course of things; by accident, unintentional. [from 16th c.]
- Not essential; incidental, secondary. [from 14th c.]
- A property which is not essential; a nonessential; anything happening accidentally.
- (music) A sharp, flat, or natural, occurring not at the commencement of a piece of music as the signature, but before a particular note.
- (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.