Certain to miss first waterway (3)
I believe the answer is:
ure
'waterway' is the definition.
(The River Ure in North Yorkshire)
'certain to miss first' is the wordplay.
'certain' becomes 'sure' (similar in meaning).
'to miss first' means to remove the first letter.
'sure' with its initial letter removed is 'URE'.
(Other definitions for ure that I've seen before include "Midge --, singer" , "Wensleydale river" , "Ripon's river" , "River at Ripon" , "River of N. Yorkshire" .)