Diamonds -- a Christmas present -- found in freezer (6)
I believe the answer is:
icebox
'freezer' is the definition.
(I've seen this before)
'diamonds a christmas present' is the wordplay.
'diamonds' becomes 'ice' (I've seen this before).
'a christmas present' becomes 'box' (I've seen this before).
'ice'+'box'='ICEBOX'
'found in' is the link.
(Other definitions for icebox that I've seen before include "Refrigerator compartment" , "fridge compartment" , "Where food is preserved" , "Insulated cabinet for storing food" , "Freezer compartment" .)