Vegetable shown in glossy with its head chopped off (4)
I believe the answer is:
leek
'vegetable' is the definition.
(leek is a kind of vegetable)
'glossy with its head chopped off' is the wordplay.
'glossy' becomes 'sleek' (synonyms).
'with its head chopped off' means to remove the first letter.
'sleek' with its first letter taken away is 'LEEK'.
'shown in' acts as a link.
(Other definitions for leek that I've seen before include "Welsh national emblem" , "Staffordshire town?" , "One of the veggies" , "Staffs. town; vegetable" , "Welsh symbolic vegetable" .)