Bill gathers information, joining unknown business (6)
I believe the answer is:
agency
'business' is the definition.
(agency is a kind of business)
'bill gathers information joining unknown' is the wordplay.
'bill' becomes 'ac'.
'gathers' is an insertion indicator.
'information' becomes 'gen' (gen is a kind of information).
'joining' is a charade indicator (letters next to each other).
'unknown' becomes 'y' (algebra).
'ac' placed around 'gen' is 'agenc'.
'agenc'+'y'='AGENCY'
(Other definitions for agency that I've seen before include "Cagney (anag.)" , "Government unit - business providing services" , "Business that works on behalf of others" , "The A in CIA" , "Bureau; action" .)