Rotter put in river for ten years (6)
I believe the answer is:
decade
'ten years' is the definition.
(a decade is ten years)
'rotter put in river' is the wordplay.
'rotter' becomes 'cad' (a cad is a dishonourable person).
'put in' indicates putting letters inside.
'river' becomes 'dee' (River Dee).
'cad' put inside 'dee' is 'DECADE'.
'for' is the link.
(Other definitions for decade that I've seen before include "Ten year period" , "Group of ten things" , "The noughties maybe" , "Series of 10 years" , "Time period" .)