### Clue: Impervious academic eats nothing (5)
### Answer: PROOF 
 ### Explanation: Impervious academic eats nothing (5)
**PROF.** ("academic") *eats* **O** ("nothing") 
*Definition is a little loose for me, as one can say that sonething is fire-proof, but I don't think you could say that it is fire-impervious?