Vegetable is cold and undercooked (5)
I believe the answer is:
chard
'vegetable' is the definition.
(I know that chard is a type of vegetable)
'cold and undercooked' is the wordplay.
'cold' becomes 'C' (eg on taps).
'and' says to put letters next to each other.
'undercooked' becomes 'hard' (something undercooked might be hard).
'c'+'hard'='CHARD'
'is' is the link.
(Other definitions for chard that I've seen before include "Vegetable; Somerset town" , "Leafy green" , "Type of beet" , "Beet with edible leaves and stalks" , "Kind of (Swiss?) beet with edible leaves" .)