Our veg is cooked? Serious! (8)
I believe the answer is:
grievous
'serious' is the definition.
('grievous' can be a synonym of 'serious')
'our veg is cooked?' is the wordplay.
'cooked?' indicates an anagram.
'our'+'veg'+'is'='ourvegis'
'ourvegis' with letters rearranged gives 'GRIEVOUS'.
(Other definitions for grievous that I've seen before include "This sort of bodily harms is serious" , "Very severe or painful" , "distressing" , "Deplorable" , "Calamitous" .)