Crossword Genius

A unique blow? (4)

Ross

I believe the answer is:

oner

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'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" .)

I've seen this clue in the Evening Standard.
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