Mental spark (4)
![Ross](/clue/static/ross-mug.min.png)
I believe the answer is:
idea
'mental spark' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for idea that I've seen before include "Sudden inspiration?" , "Thought, belief" , "Plato's Form is" , "Fancy" , "Notion in the mind" .)