A hole most dreadfully repulsive (9)
I believe the answer is:
loathsome
'repulsive' is the definition.
(thesaurus)
'a hole most dreadfully' is the wordplay.
'dreadfully' is an anagram indicator.
'a'+'hole'+'most'='aholemost'
'aholemost' anagrammed gives 'LOATHSOME'.
(Other definitions for loathsome that I've seen before include "Disgusting, nauseating" , "gross" , "Hateful" , "Horrid" , "15 [ABHORRENT]" .)