Valuable, treasured (8)
I believe the answer is:
precious
I believe this clue is a double definition.
'valuable' is the first definition.
(similar in meaning)
'treasured' is the second definition.
(I know that treasured can be written as precious)
(Other definitions for precious that I've seen before include "Cherished or of high worth" , "Of high worth or cost" , "Cherished or valuable" , "Very fastidious" , "as good as gold" .)