Very bad doctor attached to feudal arrangement (8)
I believe the answer is:
dreadful
'very bad' is the definition.
(I've seen this before)
'doctor attached to feudal arrangement' is the wordplay.
'doctor' becomes 'dr' (abbreviation).
'attached to' means one lot of letters go next to another.
'arrangement' indicates anagramming the letters.
'feudal' anagrammed gives 'eadful'.
'dr'+'eadful'='DREADFUL'
(Other definitions for dreadful that I've seen before include "Terrible" , "Appalling, awful" , "Atrocious, awful" , "Dire, alarming" , "Informally very bad, perhaps the weather" .)