Putting by for a rainy day (6)
I believe the answer is:
saving
'putting by for a rainy day' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for saving that I've seen before include "Second World War film with Tom Hanks" , "Putting by for a rainy day" , "Except; economy" , "See 18" , "Cost reduction, except" .)