Disquisition (8)
I believe the answer is:
treatise
'disquisition' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for treatise that I've seen before include "Formal piece of writing on a particular subject" , "Systematically-written formal piece" , "Learned work formally dealing with a subject" , "Learned work on particular subject" , "Written composition" .)