Very impressive river, one where nothing is good (7)
I believe the answer is:
amazing
'very impressive' is the definition.
(I've seen this before)
'river one where nothing is good' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
'nothing' could be 'z' and 'z' is found within the answer.
'good' could be 'g' (abbreviation) and 'g' is present in the answer.
The remaining letters 'aman' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for amazing that I've seen before include "Causing wonder" , "Awesome, astounding" , "Incredible" , "Very surprising, remarkable" , "Astonishing, wonderful" .)