Awkward naked fiend in popular religious establishment (12)
I believe the answer is:
inconvenient
'awkward' is the definition.
(similar in meaning)
'naked fiend in popular religious establishment' is the wordplay.
'naked' means to look at the middle letters.
'in' means one lot of letters goes inside another.
'popular' becomes 'in' ('in' can mean trendy).
'religious establishment' becomes 'convent'.
The central letters of 'fiend' are 'ien'.
'in'+'convent'='inconvent'
'ien' put inside 'inconvent' is 'INCONVENIENT'.
(Other definitions for inconvenient that I've seen before include "Inopportune" , "Causing difficulties" , "Awkward" , "Causing slight difficulty" , "Troublesome" .)