Article relative to dissertation (6)
I believe the answer is:
thesis
'dissertation' is the definition.
('thesis' can be a synonym of 'dissertation')
'article relative' is the wordplay.
'article' becomes 'the' (the 'definite article' part of speech).
'relative' becomes 'sis' (short for sister).
'the'+'sis'='THESIS'
'to' is the link.
(Other definitions for thesis that I've seen before include "Student dissertation" , "Academic essay" , "Analytical essay written for university degree" , "Article by son is in paper" , "writing following research" .)