Awful old English king secured by rope (9)
I believe the answer is:
execrable
'awful' is the definition.
(thesaurus)
'old english king secured by rope' is the wordplay.
'old' becomes 'ex'.
'english' becomes 'e' (abbreviation).
'king' becomes 'r' (r is abbreviation for rex).
'secured by' means one lot of letters goes inside another (I've seen this in other clues).
'rope' becomes 'cable' (cable is a kind of rope**).
'r' put into 'cable' is 'crable'.
'ex'+'e'+'crable'='EXECRABLE'
(Other definitions for execrable that I've seen before include "Accursed" , "Woeful" , "terrible" , "A celeb rex may be abominable" , "Dreadful" .)