Finest cannabis from the south (3)
I believe the answer is:
top
'finest' is the definition.
(I've seen this before)
'cannabis from the south' is the wordplay.
'cannabis' becomes 'pot' (synonyms).
'from the south' says the letters should be written in reverse (in a down clue, letters go up).
'pot' written backwards gives 'TOP'.
(Other definitions for top that I've seen before include "Peak; child's toy" , "SECOND PART OF 10 ACROSS" , "Children's toy" , "Apex; child's toy" , "Kill" .)