Precious material in ring worn by queen (5)
I believe the answer is:
pearl
'precious material' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'ring worn by queen' is the wordplay.
'ring' becomes 'peal' (synonyms).
'worn by' indicates putting letters inside (outside letters are worn by those on the inside).
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'peal' placed around 'r' is 'PEARL'.
'in' is the link.
Can you help me to learn more?
(Other definitions for pearl that I've seen before include "Lustrous globule prized as a gem" , "Lustrous structure inside an oyster-shell" , "one regularly in stitches" , "Small type" , "something highly valued" .)