Scoundrel has quiet word about one element (7)
I believe the answer is:
cadmium
'element' is the definition.
(cadmium is a chemical element)
'scoundrel has quiet word about one' is the wordplay.
I cannot quite see how this works, but
'scoundrel' could be 'cad' (cad is a kind of scoundrel) and 'cad' is located in the answer.
'one' could be 'i' (Roman numeral) and 'i' is present in the answer.
'quiet' could be 'mum' (to keep mum is to stay quiet) and 'mum' is present in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for cadmium that I've seen before include "cell" , "reactor component" , "Silvery-white metallic element" , "Metal used in batteries and pigments" , "Metallic element, Cd" .)