Related Clues:

• Light bulb, in comics
• Mental glimmer
• Object of thought
• Head piece?
• Creator's sine qua non
• String, for one
• Brainchild
• Outer layer of an organ
• Theory
• It comes to a head
• Creative nugget
• Exclamation point?
• Inventor's "step one"
• Sneaking suspicion
• Fava or pea