A unique blow? (4)
I believe the answer is:
oner
'blow?' is the definition.
(I have seen 'Heavy blow ' mean 'oner' so perhaps 'blow' could also mean 'oner')
'a unique' is the wordplay.
'a' becomes 'one'.
'unique' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'one'+'r'='ONER'
Can you help me to learn more?
(Other definitions for oner that I've seen before include "A quid" , "A pound coin" , "A PS1 note (colloq.)" , "Unique person" , "Heavy blow; 1 note" .)