Furious, old Rover's losing power (5)
I believe the answer is:
irate
'furious' is the definition.
(I've seen this before)
'old rover's losing power' is the wordplay.
I cannot really understand how this works, but
'rover' could be 'i' (where the crossword setter is 'Rover') and 'i' is found in the answer.
The remaining letters 'rate' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for irate that I've seen before include "Magical rod" , "Hacked off" , "Boiling" , "will be up in arms" , "Angry, annoyed" .)