Superior’s hasty departure on vessel from the east (3-6)
I believe the answer is:
top-flight
'superior's' is the definition.
(I've seen this before)
'hasty departure on vessel from the east' is the wordplay.
'hasty departure' becomes 'flight' (act of fleeing).
'on' says to put letters next to each other.
'vessel' becomes 'pot' (type of container).
'from the east' shows that the letters should be reversed in order (on a map from right to left).
'pot' back-to-front is 'top'.
'flight' put after 'top' is 'TOP-FLIGHT'.
(Other definitions for top-flight that I've seen before include "Superior" , "Of the highest class" , "Highest level" , "Excellent -- best possible" .)