Certain to miss first river (3)
I believe the answer is:
'river' is the definition.
(river in Yorkshire)
'certain to miss first' is the wordplay.
'certain' becomes 'sure' (synonyms).
'to miss first' means to remove the first letter.
'sure' with its first letter taken away is 'URE'.
(Other definitions for ure that I've seen before include "River of N. Yorkshire" , "Ripon's river" , "Wensleydale river" , "River at Ripon" , "North Yorkshire river" .)