River shut up in year before opening of Nile (7)
I believe the answer is:
shannon
'river' is the definition.
(I know that Shannon is a river)
'shut up in year before opening of nile' is the wordplay.
'shut up' becomes 'sh'.
'in' is an insertion indicator.
'year before' becomes 'anon' (I can't explain this - if you can you should give a lot more credence to this answer).
'opening of' indicates taking the first letters.
The first letter of 'nile' is 'n'.
'anon' going around 'n' is 'annon'.
'sh'+'annon'='SHANNON'
Can you help me to learn more?
(Other definitions for shannon that I've seen before include "One who rendered runaway" , "current in Ireland" , "Long-distance runner" , "Irish 10" , "Ireland's longest river" .)