Fellow's let down over drug in plant container (9)
I believe the answer is:
flowerpot
'plant container' is the definition.
(I've seen this before)
'fellow's let down over drug' is the wordplay.
'fellow' becomes 'f' (abbreviation - of a society etc.).
'let down' becomes 'lower' ('lower' can be a synonym of 'let down').
'over' means one lot of letters go next to another.
'drug' becomes 'pot' (slang term for cannabis).
'f'+'lower'+'pot'='FLOWERPOT'
'in' acts as a link.
(Other definitions for flowerpot that I've seen before include "Geranium holder?" , "What may hold" , "aid for gardeners" , "Container for plants" , "Something grows in this" .)