Church on rocky outcrop set ablaze (5)
I believe the answer is:
torch
'set ablaze' is the definition.
'church on rocky outcrop' is the wordplay.
'church' becomes 'ch' (common abbreviation).
'on' says to put letters next to each other.
'rocky outcrop' becomes 'tor' (term for a hill).
'ch' after 'tor' is 'TORCH'.
(Other definitions for torch that I've seen before include "A large candle" , "Small portable battery-powered electric lamp" , "Set fire to - hand-held light" , "Small hand-held battery lamp" , "Flashlight" .)