Vegetable giving brother terrible colic (8)
I believe the answer is:
Here is my best explanation:
'vegetable' is the definition.
(broccoli is a kind of vegetable)
'giving brother terrible colic' is the subsidiary indication.
'giving' says to put letters next to each other.
'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 "A variety of cabbage", "Type of cabbage", "A variety of brassica", "A hardy variety of cauliflower", "Green vegetable - producer of Bond films", "Sort of green cauli", "Calabrese", "Green/purplish vegetable", "Type of vegetable" and "Variety of cabbage, green heads".)