Mess remains behind hotel (4)
I believe the answer is:
hash
'mess' is the definition.
(as in making a hash of something)
'remains behind hotel' is the wordplay.
'remains' becomes 'ash' (remains of a fire).
'behind' is a charade indicator (letters next to each other).
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'ash' put after 'h' is 'HASH'.
(Other definitions for hash that I've seen before include "Keypad symbol" , "preparation that's nothing new" , "Mess; meat/potato dish" , "Recooked dish for shah" , "Stew - botched job" .)