Gather idiot has badge with end missing (8)
I believe the answer is:
assemble
'gather' is the definition.
(synonyms)
'idiot has badge with end missing' is the wordplay.
'idiot' becomes 'ass' (I've seen this before).
'has' is a charade indicator (letters next to each other).
'badge' becomes 'emblem' (I've seen this before).
'with end missing' means to remove the last letter.
'emblem' with its last letter taken off is 'emble'.
'ass'+'emble'='ASSEMBLE'
(Other definitions for assemble that I've seen before include "Meet" , "Bring/come together" , "Gather together in one place" , "Collect in one place" , "Come or bring group together" .)