Onion's cousin (4)
I believe the answer is:
leek
'onion's cousin' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for leek that I've seen before include "Edible plant, Welsh symbol" , "Welsh national emblem" , "One of the veggies" , "Eat the vegetable and keel over" , "Vegetable - Welsh symbol" .)