Accused criminal pockets new penny that is marked with a D (6,3)
I believe the answer is:
dunces cap
'accused criminal pockets new penny that is marked with a d' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'accused criminal pockets new penny' is the wordplay.
I cannot quite understand how this works, but
'new' could be 'n' (common abbreviation eg NT for New Testament) and 'n' is present in the answer.
an anagram of 'accused' is 'ducesca' which is located in the remaining letters.
'penny' could be 'p' (short for pence) and 'p' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for dunces cap that I've seen before include "Headgear used to humiliate slow learners" , "Classroom idiot's headgear" , "Ignorant boy's headgear" .)