Fool died: rest in peace (4)
I believe the answer is:
drip
'fool' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'died rest in peace' is the wordplay.
'died' becomes 'd' (abbreviation next to the year of someone's death).
'rest in peace' becomes 'RIP' (inscription written on gravestones).
'd'+'rip'='DRIP'
Can you help me to learn more?
(Other definitions for drip that I've seen before include "weak character" , "Weak and pathetic person" , "Wet - sign of faulty washer" , "wet blanket" , "Fall in small drops as from tap" .)