Empty, silly sign of agreement at meeting (5)
I believe the answer is:
synod
'meeting' is the definition.
(type of religious meeting)
'empty silly sign of agreement' is the wordplay.
'empty' suggests removing the centre.
'sign of agreement' becomes 'nod' (a nod can indicate agreement).
'silly' with its centre removed is 'sy'.
'sy'+'nod'='SYNOD'
'at' acts as a link.
(Other definitions for synod that I've seen before include "Ecclesiastical council" , "council meeting" , "Ecclesiastical gathering" , "Assembly of the clergy" , "Ecumenical council" .)