Detective showing accountant unit used by printer (4)
I believe the answer is:
pica
'by printer' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'detective showing accountant unit' is the wordplay.
I cannot quite understand how this works, but
'detective' could be 'pi' (private investigator) and 'pi' is found in the answer.
'accountant' could be 'ca' (abbreviation for chartered accountant) and 'ca' is located in the answer.
This accounts for all the letters.
This explanation may well be incorrect...
'used' is the link.
Can you help me to learn more?
(Other definitions for pica that I've seen before include "Unit of type size" , "old type" , "size related to type" , "Printing unit" , "Magpie's" .)