An old fool (6)
I believe the answer is:
jester
This might be a double definition.
'an old' is the first definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'fool' is the second definition.
(synonyms)
Can you help me to learn more?
(Other definitions for jester that I've seen before include "one entertaining in court" , "Court fool" , "Buffoon" , "Professional clown of the middle ages" , "Comic" .)