Reduce new dissertations in brackets (11)
I believe the answer is:
parentheses
'brackets' is the definition.
(I've seen this before)
'reduce new dissertations' is the wordplay.
'reduce' becomes 'pare' (I've seen this in another clue).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'dissertations' becomes 'theses' ('thesis' can be a synonym of 'dissertation').
'pare'+'n'+'theses'='PARENTHESES'
'in' acts as a link.
(Other definitions for parentheses that I've seen before include "(shown here)" , "Round brackets" .)