Obsessive sibling welcoming year in therapy (8)
I believe the answer is:
analysis
'therapy' is the definition.
(thesaurus)
'obsessive sibling welcoming year' is the wordplay.
'obsessive' becomes 'anal' (anal can mean obsessed with order).
'sibling' becomes 'sis' (short for sister).
'welcoming' is an insertion indicator (in sense of 'inviting in').
'year' becomes 'y'.
'anal'+'sis'='analsis'
'analsis' placed around 'y' is 'ANALYSIS'.
'in' is the link.
(Other definitions for analysis that I've seen before include "Detailed breakdown" , "Detailed interpretation" , "Study of mind" , "Breakdown (for study)" , "Dissection and examination" .)