### Clue: Where King John's powers were diluted with weak alcoholic drink, say? (9)
### Answer: RUNNYMEDE 
 ### Explanation: Definition: Where King John's powers were diluted
 RUNNY(flowing more easily, and therefore, for liquid substances, an indication of being diluted or weakened in concentration) + **homophone of**(…, say) "mead"(an alcoholic drink from fermented honey and water).
Answer: The meadow on the south bank of the Thames where King John was forced to sign the Magna Carta.