Fiery old flame has power: love is renewed (9)
I believe the answer is:
explosive
'fiery' is the definition.
(I've seen this before)
'old flame has power love is renewed' is the wordplay.
'old flame' becomes 'ex' (I've seen this in other clues).
'has' means one lot of letters go next to another.
'power' becomes 'p'.
'renewed' is an anagram indicator.
'love'+'is'='loveis'
'loveis' with letters rearranged gives 'losive'.
'ex'+'p'+'losive'='EXPLOSIVE'
(Other definitions for explosive that I've seen before include "Likely to cause anger or controversy" , "Likely to result in an outburst of violence" , "Eg, TNT" , "Volatile" , "Eg, gelignite" .)