Trust company wrongly fined (7)
I believe the answer is:
confide
'trust' is the definition.
(I know that trust can be written as confide)
'company wrongly fined' is the wordplay.
'company' becomes 'co' (abbreviation).
'wrongly' indicates an anagram (I've seen this in other clues).
'fined' with letters rearranged gives 'nfide'.
'co'+'nfide'='CONFIDE'
(Other definitions for confide that I've seen before include "Tell secret as to friend - mum's the word" , "Tell secret or entrust to" , "Trust wholly (in person)" , "Impart secrets to someone" .)