Feminine reserve about husband’s file (5)
I believe the answer is:
fiche
'file' is the definition.
(as in a microfiche)
'feminine reserve about husband's' is the wordplay.
'feminine' becomes 'f' (abbreviation listed in Chambers).
'reserve' becomes 'ice ' (both can mean aloofness).
'about' indicates putting letters inside.
'husband' becomes 'h' (abbreviation).
'ice' going around 'h' is 'iche'.
'f'+'iche'='FICHE'
(Other definitions for fiche that I've seen before include "Small film" , "Card bearing data" , "data store" , "Archived record" , "bit of film" .)