Class adopts one word for flower container? (9)
I believe the answer is:
'class adopts one word' is the definition.
I can't judge whether this definition defines the answer.
'flower container?' is the wordplay.
'flower' becomes 'river' (A river flows and is therefore a flower).
'container?' becomes 'bank' (bank is a kind of container).
'for' acts as a link.
Can you help me to learn more?
(Other definitions for riverbank that I've seen before include "where those rowing may end up" , "home of the vole" , "where our Parliament stands" .)