Obsessive year is involving special research (8)
I believe the answer is:
analysis
'research' is the definition.
(thesaurus)
'obsessive year is involving special' is the wordplay.
'obsessive' becomes 'anal' (I've seen this before).
'year' becomes 'y'.
'involving' is an insertion indicator.
'special' becomes 'S' (common abbreviation as in Special Air Service).
'y'+'is'='yis'
'yis' placed around 's' is 'ysis'.
'anal'+'ysis'='ANALYSIS'
(Other definitions for analysis that I've seen before include "A taking apart for examination" , "resolution" , "Study of mind" , "Criticism" , "Dissection and examination" .)