Leave a vessel at the pithead (4)
I believe the answer is:
park
'leave' is the definition.
(parking a car is leaving it somewhere)
'a vessel at the pithead' is the wordplay.
'a vessel' becomes 'ark' (ark is a kind of vessel).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'the pithead' becomes 'p' (head letter of 'pit').
'ark' put after 'p' is 'PARK'.
(Other definitions for park that I've seen before include "Public gardens" , "One who explored the Niger" , "Pleasure garden" , "Leave car - recreational area" , "Area for recreation in a city" .)