Religion in Wiltshire regularly occupying various imams (9)
I believe the answer is:
mithraism
'religion' is the definition.
(Mithraism is an example)
'wiltshire regularly occupying various imams' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'occupying' indicates putting letters inside.
'various' is an anagram indicator.
The alternating letters of 'wiltshire' are 'ithr'.
'imams' is an anagram of 'maism'.
'ithr' going inside 'maism' is 'MITHRAISM'.
'in' acts as a link.
(Another definition for mithraism that I've seen is " Religion".)