Powerful cut behind ending in catch, grrrr! (8)
I believe the answer is:
harrumph
'grrrr' is the definition.
I can't tell whether this defines the answer.
'powerful cut behind ending in catch' is the wordplay.
'powerful cut' becomes 'har' (I am not sure about this - if you are sure you should believe this answer much more).
'behind' becomes 'rump' (informal term for the buttocks).
'ending in' says to take the final letters.
The final letter of 'catch' is 'h'.
'har'+'rump'+'h'='HARRUMPH'
Can you help me to learn more?
(Other definitions for harrumph that I've seen before include "Express grumpy opposition" , "Make disapproving sound" , "Sound of someone clearing throat" , "Clear one's throat noisily" , "Show disapproval" .)