Element in strangely plush ancient city (7)
I believe the answer is:
sulphur
'element' is the definition.
(I know that sulphur is a type of element)
'strangely plush ancient city' is the wordplay.
'strangely' indicates an anagram.
'ancient city' becomes 'ur' (ancient Sumerian city state).
'plush' anagrammed gives 'sulph'.
'sulph'+'ur'='SULPHUR'
'in' acts as a link.
(Other definitions for sulphur that I've seen before include "Highly flammable yellow element" , "S (chem.)" , "Yellow non-metallic element" , "Chemical used in match heads" , "Chemical element" .)