Vegetable in line that's scary! (4)
I believe the answer is:
leek
'vegetable' is the definition.
(leek is a kind of vegetable)
'line that's scary' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'that's scary' becomes 'eek' (exclamation of fear).
'l'+'eek'='LEEK'
'in' is the link.
(Other definitions for leek that I've seen before include "Plant; Welsh emblem" , "Vegetable of the onion family" , "One of the veggies" , "what Fluellen wore in France?" , "National emblem of Wales." .)