### Clue: Fortuitous bit of scoring? (10)
### Answer: ACCIDENTAL 
 ### Explanation: Definition: Fortuitous
Double definition – in music an accidental is a flat or sharp sign (or similar) that indicates that a note isn't to played as in the key signature. Nice to see the "correct" use of "fortuitous" in the other definition as "by chance" rather than the increasingly-common "fortunately".