Ex-boozers keeping port, not started, in vessel (5)
I believe the answer is:
'vessel' is the definition.
'ex-boozers keeping port not started' is the wordplay.
'ex boozers' becomes 'aa' (I can't justify this - if you can you should give a lot more credence to this answer).
'keeping' means one lot of letters goes inside another.
'not started' means to remove the first letter (I've seen 'not starting' mean this).
'port' with its initial letter taken off is 'ort'.
'aa' going around 'ort' is 'AORTA'.
'in' is the link.
Can you help me to learn more?
(Other definitions for aorta that I've seen before include "Tube" , "blood flows from it" , "Trunk route" , "Great artery in body" , "Large trunk artery" .)