Mafia boss had to chip in (6)
I believe the answer is:
donate
'chip in' is the definition.
(thesaurus)
'mafia boss had' is the wordplay.
'mafia boss' becomes 'don' (I've seen this before).
'had' becomes 'ate' (e.g. I had an ice cream).
'don'+'ate'='DONATE'
'to' is the link.
(Other definitions for donate that I've seen before include "Make an offer" , "Give charitably - say blood" , "Contribute (to charity)" , "Give as a gift as to charity" , "Atoned (anag)" .)