Valuable stone (3)
I believe the answer is:
gem
'valuable stone' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for gem that I've seen before include "A jewel or precious stone" , "Setter might bed this" , "Precious or semi-precious stone" , "A jewel of an Orangeman" , "Valued person; jewel" .)