Sounds like a stupid trick with a non-metallic element (7)
I believe the answer is:
silicon
'element' is the definition.
(I know that silicon is a type of metalloid)
'sounds like a stupid trick with a non-metallic' is the wordplay.
I cannot really understand how this works, but
'trick' could be 'con' (a con is a fraud or trick) and 'con' is found in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for silicon that I've seen before include "Chip substrate element" , "Element found in chips?" , "Element used in integrated circuits" , "Californian valley" , "Semiconducting element" .)