Necklace identified in lecture on radio (4)
I believe the answer is:
torc
'necklace' is the definition.
(medieval neck ornament)
'lecture on radio' is the wordplay.
'lecture' becomes 'talk' (synonyms).
'on radio' indicates a 'sounds like' (homophone) clue.
'talk' sounds like 'TORC'.
'identified in' acts as a link.
(Other definitions for torc that I've seen before include "Metal neck ornament of ancient Britons" , "Metallic neck ornament" , "ancient necklace" , "Rigid circular necklace" , "Metal armband worn by Ancient Britons" .)