Ghastly Blunt, essentially overcome by terrible flaw (5)
I believe the answer is:
awful
'ghastly' is the definition.
(I've seen this before)
'blunt essentially overcome by terrible flaw' is the wordplay.
'essentially' indicates the central letters.
'overcome by' indicates putting letters inside.
'terrible' indicates an anagram.
The middle of 'blunt' is 'u'.
'flaw' is an anagram of 'awfl'.
'u' put into 'awfl' is 'AWFUL'.
(Other definitions for awful that I've seen before include "pants" , "Very poor" , "Horrific" , "Fearsome" , "shocking" .)