Noble song written about departed leader (4)
I believe the answer is:
lady
'noble' is the definition.
(I've seen this before)
'song written about departed leader' is the wordplay.
'song' becomes 'lay' (poetic term for a song).
'written about' means one lot of letters goes inside another.
'leader' indicates taking the first letters.
The first letter of 'departed' is 'd'.
'lay' placed around 'd' is 'LADY'.
(Other definitions for lady that I've seen before include "Woman, maybe titled" , "mature woman" , "Title for a knight's wife" , "Woman, of refinement perhaps" , "Gentlewoman" .)