Conductor unknown in Cuba (4)
I believe the answer is:
zinc
'conductor' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'unknown in cuba' is the wordplay.
'unknown' becomes 'z' (represents an unknown value in algebra).
'cuba' becomes 'c'.
'z'+'in'+'c'='ZINC'
Can you help me to learn more?
(Other definitions for zinc that I've seen before include "White metallic element used in alloys" , "Type of metal" , "Metal used for galvanising steel" , "Blue-white metallic element, atomic number 30" , "Ingredient in brass" .)