River appeared without end (3)
I believe the answer is:
cam
'river' is the definition.
(river in Cambridge, England)
'appeared without end' is the wordplay.
'appeared' becomes 'came' (I've seen this before).
'without end' means to remove the last letter.
'came' with its last letter taken away is 'CAM'.
(Other definitions for cam that I've seen before include "River also called Granta" , "Eccentric contrivance" , "Rotating mechanism" , "Projection on rotating cylinder" , "running into Great Ouse?" .)