A worn key in a gold case (5)
I believe the answer is:
gilet
This clue could be a double definition.
'a worn key' is the first definition.
The definition suggests a singular noun which matches the answer.
'gold case' is the second definition.
The definition suggests a singular noun which matches the answer.
'in a' is the link.
Can you help me to learn more?
(Other definitions for gilet that I've seen before include "Body-warmer" , "Waistcoat" , "apparel" , "Sleeveless padded jacket" , "Type of jacket" .)