Crossword Genius

Vessel, one that suddenly goes up and down? (7)

Ross

I believe the answer is:

pitcher

I'm a little stuck... Click here to teach me more about this clue!

'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?" .)

I've seen this clue in The Guardian.
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