Around a river, sailor paddles (4)
I believe the answer is:
oars
'paddles' is the definition.
(I've seen this before)
'around a river sailor' is the wordplay.
'around' means one lot of letters goes inside another.
'river' becomes 'r'.
'sailor' becomes 'os' (ordinary seaman).
'a'+'r'='ar'
'ar' placed into 'os' is 'OARS'.
(Other definitions for oars that I've seen before include "Propelling implements" , "Manual boat propellers" , "Soar with propellors" , "Soar around the rowers" , "Sculls" .)