Complex operation involves protracted dissection (4,8)
I believe the answer is:
long division
'dissection' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Maybe there's an association between them I don't understand?
'complex operation involves protracted' is the wordplay.
I cannot quite see how this works, but
'operation' could be 'division' (division is a kind of operation) and 'division' is found within the answer.
'protracted' could be 'long' (similar in meaning) and 'long' is located in 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 long division that I've seen before include "Mathematical calculation" , "result of vendetta?" , "(Pre-calculator) arithmetical process" , "Arithmetic" , "Mathematical operation" .)