Not demanding retiring copper must take the lead (5)
I believe the answer is:
cushy
'not demanding' is the definition.
(I've seen this before)
'retiring copper must take the lead' is the wordplay.
'retiring' becomes 'shy' (both can mean reserved or introverted).
'copper' becomes 'cu' (chemical symbol).
'must take the lead' says to put letters next to each other (some letters go at the front).
'shy' after 'cu' is 'CUSHY'.
(Other definitions for cushy that I've seen before include "Undemanding, easy" , "16 21 [INDIAN IMPORT]" , "Easy, soft (colloq.)" , "Undemanding, secure" , "Jammy" .)