Considerably above average (5)
I believe the answer is:
great
'considerably above average' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for great that I've seen before include "Enormous" , "Dickens novel about Pip" , "Peter the -, Russ. tsar" , "Marvellous; big" , "Brunel's third and last steamship" .)