Break back carrying wife's deposits as security (5)
I believe the answer is:
pawns
'deposits as security' is the definition.
'break back carrying wife's' is the wordplay.
'break' becomes 'snap' (snapping is a kind of breaking).
'back' says the letters should be written backwards.
'carrying' means one lot of letters goes inside another.
'wife' becomes 'w'.
'snap' backwards is 'pans'.
'pans' enclosing 'w' is 'PAWNS'.
(Other definitions for pawns that I've seen before include "made pledges" , "The foot-soldiers in chess" , "Minor chessmen" , "Puts into hock" , "Chess pieces" .)