### Clue: Flower seller's first flower show in Covent Garden? (8)
### Answer: FALSTAFF 
 ### Explanation: Definition: show in Covent Garden
 FAL(the Cornish river;flow-er) + **the 1st letter of**(…'s first) "seller's" + TAFF(the Welsh river;flow-er).
Defn: An opera, possibly performed in the Royal Opera House in Covent Garden.