Busy English cardinal hosts very large society (9)
I believe the answer is:
engrossed
'busy' is the definition.
(thesaurus)
'english cardinal hosts very large society' is the wordplay.
'english' becomes 'eng'.
'cardinal' becomes 'red' (I've seen this in other clues).
'hosts' is an insertion indicator.
'very large' becomes 'os' (abbreviation for oversize).
'society' becomes 's' (common abbreviation in names of organisations).
'os'+'s'='oss'
'red' placed around 'oss' is 'rossed'.
'eng'+'rossed'='ENGROSSED'
(Other definitions for engrossed that I've seen before include "Preoccupied" , "Gripped" , "occupied" , "Deeply engaged" , "Totally absorbed" .)