Sword of thin aluminium? (4)
I believe the answer is:
foil
'sword' is the definition.
(foil is a kind of sword)
'of thin aluminium?' is the wordplay.
I cannot quite understand how this works, but
'of' could be 'o' and 'o' is located in the answer.
The remaining letters 'fil' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for foil that I've seen before include "hamper" , "Blunt sword with a button on the end" , "Prevent from succeeding" , "Thwart - contrasting thing - sword" , "Check" .)