Secret society forming friends (9)
I believe the answer is:
intimates
'friends' is the definition.
(intimate is a kind of friend)
'secret society' is the wordplay.
I cannot really see how this works, but
'society' could be 's' (common abbreviation in names of organisations) and 's' is found within the answer.
The remaining letters 'intimate' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'forming' is the link.
Can you help me to learn more?
(Another definition for intimates that I've seen is " Hints - close friends".)