King's awful dread about onset of war (6)
I believe the answer is:
edward
'king's' is the definition.
(I've seen this before)
'awful dread about onset of war' is the wordplay.
'awful' indicates an anagram.
'about' indicates putting letters inside.
'onset of' indicates taking the first letters.
The first letter of 'war' is 'w'.
'dread' anagrammed gives 'edard'.
'edard' going around 'w' is 'EDWARD'.
(Other definitions for edward that I've seen before include "Lear, Elgar or Fox" , "Boy's name" , "The Black Prince's name" , "Male name" , "The Black Prince" .)