Held in reserve (6)
I believe the answer is:
stored
'held in reserve' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for stored that I've seen before include "Stashed away" , "Squirrelled away" , "Warehoused" , "Saved up in Dorset" , "Kept for future use, as in warehouse" .)