Disquisition (6)
'disquisition' is the definition.
(I've seen this before)
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" .)
'disquisition' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for thesis that I've seen before include "theory" , "Treatise advancing a new point of view resulting from research" , "Learned dissertation" , "Subject" , "writing following research" .)