The most common and most likely answer to this crossword clue is the 8 plus 5 letter word TREASURE CHEST
I've seen this crossword clue in The Daily Telegraph
T
R
E
A
S
U
R
E
C
H
E
S
T
More clues leading to the result TREASURE CHEST
- Valuable box: safe found in stretch in river
- Valuable box sure to be in the crates at sea
- ‘X’ on map might show whereabouts of this diabolical theatre’s curse
- Rescues the art neglected in a valuable box
- Trustees reach out, finding valuable hidden store
- Doctor takes certain pains, refuses a box of goodies
- Valuable box certain to be found among the crates at sea
Buddy explains!
The straight part
We know that "valuable hidden store" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case valuable hidden store = treasure chest.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.