Relative in finance (3)
I believe the answer is:
nan
'relative' is the definition.
(informal term for a grandmother)
'in finance' is the wordplay.
'in' indicates a hidden word.
'NAN' is hidden within 'finance'.
(Other definitions for nan that I've seen before include "Type of Indian bread" , "type of slightly leavened bread" , "Granny; bread" , "Grandmother (informal)" , "Gran" .)