Paddle with duck alongside a river (3)
I believe the answer is:
'paddle' is the definition.
(I've seen this before)
'duck alongside a river' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'alongside' says to put letters next to each other.
'river' becomes 'r' (abbreviation for river).
'with' is the link.
(Other definitions for oar that I've seen before include "Pole for rowing" , "Rower" , "Sportsman" , "One of an eight" , "Rowing device" .)