A guy's gone off to find a religious assembly (9)
I believe the answer is:
synagogue
'a religious assembly' is the definition.
(I've seen this before)
'a guy's gone off' is the wordplay.
'off' indicates an anagram.
'a'+'guys'+'gone'='aguysgone'
'aguysgone' with letters rearranged gives 'SYNAGOGUE'.
'to find' is the link.
(Other definitions for synagogue that I've seen before include "Place for public Jewish worship" , "Jewish house of worship" , "Place of worship for Jewish congregation" , "religious building" , "Worshippers" .)