Most important vessel coming from the East (3)
I believe the answer is:
top
'most important' is the definition.
'vessel coming from the east' is the wordplay.
'vessel' becomes 'pot' (pot is a kind of vessel).
'coming from the east' is a reversal indicator (letters written from right to left or east to west).
'pot' written backwards gives 'TOP'.
(Other definitions for top that I've seen before include "Highest part" , "premier" , "Summit, peak" , "Peak; beat" , "jumper, say?" .)