Stretch - of river? (5)
I believe the answer is:
reach
I believe this is a double definition.
'stretch' is the first definition.
(I know that stretch can be written as reach)
'river?' is the second definition.
(I know that reach is a type of river)
'of' acts as a link.
(Other definitions for reach that I've seen before include "It's an advantage for a boxer" , "Get in touch" , "Arrive at; extend to" , "Stretch of river: achieve" , "Arrive at (a place)" .)