Nothing at the end of grim Iberian river (5)
I believe the answer is:
douro
'iberian river' is the definition.
(I've seen this in another clue)
'nothing at the end of grim' is the wordplay.
'nothing' becomes 'O' (looks like zero - 0).
'at the end of' is a charade indicator (letters next to each other).
'grim' becomes 'dour' (synonyms).
'o' put after 'dour' is 'DOURO'.
(Other definitions for douro that I've seen before include "Iberian river" , "European runner" , "Hollow bubbling sound" .)