Funeral song to stop incorporating reflection of old King (5)
I believe the answer is:
dirge
'funeral song' is the definition.
(I've seen this in another clue)
'stop incorporating reflection of old king' is the wordplay.
'stop' becomes 'die' (as in a machine stopping or dying).
'incorporating' is an insertion indicator.
'reflection of' shows that the letters should be reversed in order (I've seen 'reflection' mean this).
'old king' becomes 'GR' (Georgius Rex, Latin for King George).
'gr' back-to-front is 'rg'.
'die' going around 'rg' is 'DIRGE'.
'to' acts as a link.
(Other definitions for dirge that I've seen before include "Dragging piece" , "Funeral hymn" , "A depressing number" , "Keen; lament" , "A slow mournful song, lament for the dead" .)