Colonist taking bench by river (7)
I believe the answer is:
settler
'colonist' is the definition.
('settler' can be a synonym of 'colonist')
'bench by river' is the wordplay.
'bench' becomes 'settle' (settle is a kind of bench).
'by' means one lot of letters go next to another.
'river' becomes 'r'.
'settle'+'r'='SETTLER'
'taking' acts as a link.
(Other definitions for settler that I've seen before include "One taking up residence in a new area" , "decisive blow" , "who pays his bills" , "One colonising new area" , "Early colonist" .)