Furious, I rebuke (5)
I believe the answer is:
irate
'furious' is the definition.
(I know that furious can be written as irate)
'i rebuke' is the wordplay.
'rebuke' becomes 'rate' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'i'+'rate'='IRATE'
Can you help me to learn more?
(Other definitions for irate that I've seen before include "Hacked off" , "Angry and incensed" , "Spitting feathers" , "Magical rod" , "A tier (anag)" .)