Uncommunicative about one being faced by rogue element (7)
I believe the answer is:
cadmium
'element' is the definition.
(cadmium is a chemical element)
'uncommunicative about one being faced by rogue' is the wordplay.
'uncommunicative' becomes 'mum' (similar in meaning).
'about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'being faced by' says to put letters next to each other.
'rogue' becomes 'cad' (I've seen this in another clue).
'mum' enclosing 'i' is 'mium'.
'mium' after 'cad' is 'CADMIUM'.
(Other definitions for cadmium that I've seen before include "A yellow" , "Soft bluish-white metallic element" , "reactor component" , "Metal resembling zinc" , "Metal used in batteries and pigments" .)