Leading Roman Catholic staying in a hotel (4)
I believe the answer is:
arch
'leading' is the definition.
(e.g. in arch-enemy)
'roman catholic staying in a hotel' is the wordplay.
'roman catholic' becomes 'rc' (abbreviation for Roman Catholic).
'staying in' is an insertion indicator.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'a'+'h'='ah'
'rc' going inside 'ah' is 'ARCH'.
(Other definitions for arch that I've seen before include "Main" , "Way though - on foot!" , "Prefix meaning cheif, perhaps enemy" , "part of fingerprint" , "This enemy is major" .)