Special gift almost certainly something valuable (8)
I believe the answer is:
treasure
'something valuable' is the definition.
'special gift almost certainly' is the wordplay.
'special gift' becomes 'treat'.
'almost' means to remove the last letter (most of the word but not all of it).
'certainly' becomes 'sure' ('sure' can be a synonym of 'certainly').
'treat' with its final letter removed is 'trea'.
'trea'+'sure'='TREASURE'
(Other definitions for treasure that I've seen before include "Cherish like heap of valuables" , "R L Stevenson's island" , "Store of valuables" , "Stored-up wealth" , "Prize highly" .)