Huge blunder if one's in court, having been set up (8)
I believe the answer is:
terrific
'huge' is the definition.
(I've seen this before)
'blunder if one's in court having been set up' is the wordplay.
I cannot really understand how this works, but
'blunder' could be 'err' (I've seen this before) and 'err' is found within the answer.
'if' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for terrific that I've seen before include "Enormous" , "Splendid" , "Magnificent" , "Awesome" , "Excellent; of great size" .)