Convocation skilfully securing overthrow of disorderly state (8)
I believe the answer is:
assembly
'convocation' is the definition.
(thesaurus)
'skilfully securing overthrow of disorderly state' is the wordplay.
'skilfully' becomes 'ably'.
'securing' is an insertion indicator.
'overthrow of' says the letters should be written in reverse (I've seen 'overthrowing' mean this).
'disorderly state' becomes 'mess' (I've seen this before).
'mess' reversed gives 'ssem'.
'ably' placed around 'ssem' is 'ASSEMBLY'.
(Other definitions for assembly that I've seen before include "start of day at school" , "A gathering for formal meeting" , "This line is a sequence of machines and workers" , "Meeting or fitting of parts together" , "Group gathered together for a common purpose" .)