### Clue: Quietly left off plaque with date incorrectly cut for watercourse (8)
### Answer: AQUEDUCT 
 ### Explanation: Definition: watercourse
 ["p"(abbrev. for "piano", the musical direction to play quietly) + "l"(abbrev. for "left")] **deleted from**(off) "plaque" **plus**(with) D(abbrev. for "date") + **anagram of**(incorrectly) CUT.