Religious group with 100 in clique (4)
I believe the answer is:
sect
'religious group' is the definition.
(I've seen this before)
'100 in clique' is the wordplay.
'100' becomes 'c' (roman numeral).
'in' is an insertion indicator.
'clique' becomes 'set' (I've seen this before).
'c' put into 'set' is 'SECT'.
'with' acts as a link.
(Other definitions for sect that I've seen before include "Small group with own religious beliefs" , "Body of followers" , "Group of people with unusual religious beliefs" , "Subdivision of a religion" , "Breakaway group" .)