### Clue: Fine letter from 13 that's brought on board? (4)
### Answer: FETA 
 ### Explanation: Definition: that's brought on board?
**F** (fine) + **ETA** (Greek letter, so would have been found in ("from") Plato (the answer to 13ac)'s writings. 
*The board referred to in the clue is of course a cheeseboard.