Discuss stick trapped in river (6)
I believe the answer is:
debate
'discuss' is the definition.
(I've seen this before)
'stick trapped in river' is the wordplay.
'stick' becomes 'bat' (bat is a kind of stick**).
'trapped in' means one lot of letters goes inside another.
'river' becomes 'dee' (River Dee).
'bat' placed inside 'dee' is 'DEBATE'.
(Other definitions for debate that I've seen before include "Argue a point" , "Ponder" , "Discussion throung argument" , "Public argument" , "Talk" .)