Vegetable caused one to keel over? (4)

I believe the answer is:

leek

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

'caused one to keel over?' is the wordplay.
'keel' can be anagrammed to 'LEEK'.
Though, I am unsure how this is indicated.

Can you help me to learn more?

(Other definitions for leek that I've seen before include "English town" , "Edible plant, Welsh symbol" , "Vegetable related to onions" , "Vegetable emblem of Wales" , "Plant related to the onion, pair with potato for soup" .)

I've seen this clue in The Irish Times.

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