Dreadful fare cooked, not all (8)
I believe the answer is:
fearsome
'dreadful' is the definition.
(I know that dreadful can be written as fearsome)
'fare cooked not all' is the wordplay.
'cooked' is an anagram indicator (letters cooked into a new form).
'not all' becomes 'some' ('some' is the opposite to 'all').
'fare' with letters rearranged gives 'fear'.
'fear'+'some'='FEARSOME'
(Other definitions for fearsome that I've seen before include "Daunting" , "Frightful" , "Dreadful" , "Horrendous" , "Formidable" .)