Incredibly nosy duke in meeting (5)
I believe the answer is:
synod
'meeting' is the definition.
(type of religious meeting)
'incredibly nosy duke' is the wordplay.
'incredibly' indicates anagramming the letters.
'duke' becomes 'd' (abbreviation).
'nosy' is an anagram of 'syno'.
'syno'+'d'='SYNOD'
'in' acts as a link.
(Other definitions for synod that I've seen before include "Ecclesiastical assembly" , "Ecumenical council" , "Council of clergy to discuss policy" , "Clerical assembly" , "cloth gathered here" .)