Something of singular impact (4)
I believe the answer is:
oner
'something of' is the definition.
I can't judge whether this defines the answer.
'singular impact' is the wordplay.
'singular' becomes 'one' (synonyms).
'impact' becomes 'r' (I can't explain this - if you can you should believe this answer much more).
'one'+'r'='ONER'
Can you help me to learn more?
(Other definitions for oner that I've seen before include "Big blow" , "Remarkable thing" , "Out-of-date banknote" , "expert" , "A pound coin" .)