Ridicule is free in river (6)
I believe the answer is:
deride
'ridicule' is the definition.
(to deride is to ridicule or mock)
'free in river' is the wordplay.
'free' becomes 'rid' (to be free of something is to be rid of it).
'in' means one lot of letters goes inside another.
'river' becomes 'dee' (River Dee).
'rid' placed within 'dee' is 'DERIDE'.
'is' is the link.
(Other definitions for deride that I've seen before include "Speak of with contempt" , "Knock" , "Jeer, belittle" , "Express contempt for" , "Laugh at or make fun of" .)