First vessel from the east (3)
I believe the answer is:
top
'first' is the definition.
(synonyms)
'vessel from the east' is the wordplay.
'vessel' becomes 'pot' (pot is a kind of vessel).
'from the east' is a reversal indicator.
'pot' reversed gives 'TOP'.
(Other definitions for top that I've seen before include "Finest" , "cap and > sweater" , "Children's toy" , "Acme or apex" , "Spinner" .)