Wrath of king during spell without power (7)
I believe the answer is:
outrage
'wrath' is the definition.
(thesaurus)
'king during spell without power' is the wordplay.
'king' becomes 'r' (r is abbreviation for rex).
'during' is an insertion indicator.
'spell without power' becomes 'outage'.
'r' put within 'outage' is 'OUTRAGE'.
'of' is the link.
(Other definitions for outrage that I've seen before include "furious reaction" , "Profound indignation" , "Shocked anger" , "Gross violation of decency" , "scandalous!" .)