Rate about certain hoard (8)
I believe the answer is:
treasure
'hoard' is the definition.
(I have seen 'Valuable hoard ' mean 'treasure' so perhaps 'hoard' could also mean 'treasure')
'rate about certain' is the wordplay.
'about' indicates an anagram.
'certain' becomes 'sure' (synonyms).
'rate' is an anagram of 'trea'.
'trea'+'sure'='TREASURE'
(Other definitions for treasure that I've seen before include "X marks its spot!" , "Hoarded riches" , "Store of valuables" , "Accumulated riches" , "... story by R.L. Stevenson" .)