Vessel, one that suddenly goes up and down? (7)
I believe the answer is:
pitcher
'vessel' is the definition.
(I know that pitcher is a type of vessel)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for pitcher that I've seen before include "able to hold a lot of beer" , "Earthenware jug" , "Baseball bowler and container for liquid" , "Someone promoting" , "one tries to sell in a market?" .)