Related Clues:
- Lunatic, slangily
- Acorn, for one
- Head of Brazil, perhaps
- Hollow fastener
- Fruit container turned over
- Fruit served with a cracker?
- Hexagonal hardware
- Venture-launching cost, informally
- It may be busted in bed
- Wackadoodle
- Tough thing to crack
- Pecan, for one
- Fruitcake fruit
- "Headcase" is regularly used in insults
- Energy bar bit