A police officer taken in by odd element (6)
I believe the answer is:
radium
'element' is the definition.
(radium is a kind of element)
'a police officer taken in by odd' is the wordplay.
'police officer' becomes 'DI' (detective inspector).
'taken in by' indicates putting letters inside.
'odd' becomes 'rum' (rum can mean strange or dubious).
'a'+'di'='adi'
'adi' inserted within 'rum' is 'RADIUM'.
(Other definitions for radium that I've seen before include "Radioactive metal" , "Radioactive metallic element found in pitchblende" , "Metallic element discovered by the Curies" , "Radioactive element discovered by the Curies" , "Chemical element, Ra" .)