Some brief is called in relating to financial matters (6)
I believe the answer is:
fiscal
'relating to financial matters' is the definition.
'some brief is called' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'FISCAL' can be found hidden inside 'brief is called'.
'in' is the link.
(Other definitions for fiscal that I've seen before include "Related to taxes" , "In respect of tax revenues" , "Budgetary" , "Relating to state revenue" , "Involving financial matters" .)