Do replace content in slang with established language (7)
I believe the answer is:
shindig
'do' is the definition.
(I've seen this before)
'replace content in slang with established language' is the wordplay.
I cannot quite see how this works, but
'content' could be 'dig' (dig is a kind of content) and 'dig' is found within the answer.
'in' is within the answer.
The remaining letters 'sh' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for shindig that I've seen before include "wild party" , "Large, lively party" , "Lively party, knees-up" , "Lively celebration (informal)" , "Bash" .)