Fails to convert captain in matters financial (6)
I believe the answer is:
fiscal
'financial' is the definition.
(synonyms)
'fails to convert captain in' is the wordplay.
'to convert' is an anagram indicator (I've seen 'converts' mean this).
'captain' becomes 'c' (this could be a standard abbreviation I've not previously seen).
'in' is an insertion indicator.
'fails' with letters rearranged gives 'fisal'.
'fisal' placed around 'c' is 'FISCAL'.
'matters' is the link.
I am not very happy about this link. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for fiscal that I've seen before include "Relating to tax" , "For monetary gain" , "To do with public revenue of califs" , "Related to taxes" , "Califs (anag.)" .)