Stand by one entering temple (4)
I believe the answer is:
wait
'stand by' is the definition.
(I've seen this in another clue)
'one entering temple' is the wordplay.
'one' becomes 'i' (Roman numeral).
'entering' means one lot of letters goes inside another.
'temple' becomes 'wat' (type of Asian temple eg Angkor Wat).
'i' placed within 'wat' is 'WAIT'.
(Other definitions for wait that I've seen before include "Hang about" , "Be deferred" , "singer" , "Attend, expect" , "Serve at table" .)