Expel the unofficial seller going round a vessel (4,3)
I believe the answer is:
turn out
'expel' is the definition.
(synonyms)
'the unofficial seller going round a vessel' is the wordplay.
'the unofficial seller' becomes 'tout' (tout is a kind of seller. I am not sure about the 'unofficial' bit.).
'going round' is an insertion indicator.
'a vessel' becomes 'urn' (urn is a kind of vessel).
'tout' placed around 'urn' is 'TURN-OUT'.
Can you help me to learn more?
(Other definitions for turn out that I've seen before include "A number at meeting" , "assembly" , "Prove" , "End up" , "Eject" .)