An old fool (6)
I believe the answer is:
jester
This clue could be a double definition.
'an old' is the first definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.
'fool' is the second definition.
('jester' can be a synonym of 'fool')
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" .)