Vegetable in need of a plug we hear (4)

I believe the answer is:

leek

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'vegetable' is the definition.
(I know that leek is a type of vegetable)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for leek that I've seen before include "Onion-like vegetable" , "Bulb" , "Plant related to the onion, pair with potato for soup" , "Foodstuff" , "Staffs. town; vegetable" .)

I've seen this clue in The Globe and Mail.

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