Vegetable giving brother terrible colic (8)
I believe the answer is:
broccoli
'vegetable' is the definition.
(broccoli is a kind of vegetable)
'giving brother terrible colic' is the wordplay.
'giving' means one lot of letters go next to another.
'brother' becomes 'bro'.
'terrible' indicates an anagram.
'colic' is an anagram of 'ccoli'.
'bro' next to 'ccoli' is 'BROCCOLI'.
(Other definitions for broccoli that I've seen before include "Variety of cabbage, green heads" , "A hardy variety of cauliflower" , "Type of vegetable" , "Food" , "Type of cabbage" .)