### Clue: Black tree and dead tree rot (10)
### Answer: BALDERDASH 
 ### Explanation: Definition: rot
  B(black) ALDER(any tree of the genus Alnus, related to the birch) D($$d$$ead) ASH(any tree of the genus Fraxinus, related to the olive and the lilac)
Answer:  A relatively restrained way of saying "Nonsense!"