As an American, I'm extremely sceptical about vegetable! (9)
I believe the answer is:
mangetout
'vegetable' is the definition.
(I've seen this before)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for mangetout that I've seen before include "Edible pea pods" , "something on the plate" , "Vegetable" , "Sugar peas" , "From this pod" .)