Fifth of November is pigsty, full of messy ash - grotesque (9)
I believe the answer is:
misshapen
'grotesque' is the definition.
(thesaurus)
'fifth of november is pigsty full of messy ash' is the wordplay.
'fifth of november' becomes 'm' (fifth letter of the word 'November').
'pigsty' becomes 'pen' (I've seen this in another clue).
'full of' indicates putting letters inside.
'messy' indicates anagramming the letters.
'is'+'pen'='ispen'
'ash' is an anagram of 'sha'.
'ispen' enclosing 'sha' is 'isshapen'.
'm'+'isshapen'='MISSHAPEN'
(Other definitions for misshapen that I've seen before include "Unnaturally formed" , "Not looking round" , "Badly formed" , "Ugly in form" , "showing bad form" .)