Academy for code-cracking (2-2)
I believe the answer is:
co-ed
'academy' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'code-cracking' is the wordplay.
'cracking' is an anagram indicator.
'code' is an anagram of 'CO-ED'.
'for' is the link.
Can you help me to learn more?
(Other definitions for co-ed that I've seen before include "School for both sexes" , "School for boys and girls, in short" , "Teaching both girls and boys" , "Teaching attended by both sexes" .)