### Clue: Boat on lake's broad and slow (5)
### Answer: LARGO 
 ### Explanation: Definition: broad and slow
  ARGO(legendary boat,ship even, on which Jason, our setter's namesake, and company sailed in search of the Golden Fleece) **placed after**(on) L($$l$$ake)
Defn:  A musical instruction to play the passage slow in a broad and dignified manner.