King Edward's burning (3)
I believe the answer is:
red
'burning' is the definition.
(thesaurus)
'king edward's' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex**).
'edward' becomes 'ed'.
'r'+'ed'='RED'
(Other definitions for red that I've seen before include "Primary colour" , "Colour of blood" , "River, its source in the US, flowing north to empty into L Winnipeg" , "Colour of a cardinal's hat" , "lefty" .)