Theory; dissertation (6)
I believe the answer is:
thesis
I believe this is a double definition.
'theory' is the first definition.
(I've seen this before)
'dissertation' is the second definition.
(I know that dissertation can be written as thesis)
(Other definitions for thesis that I've seen before include "Theme for an essay" , "Scholarly dissertation" , "writing following research" , "Analytical essay written for university degree" , "Learned dissertation" .)