Large room in hotel? Entirely (4)
I believe the answer is:
hall
'large room' is the definition.
(a hall is a large room)
'hotel? entirely' is the wordplay.
'hotel?' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'entirely' becomes 'all' (all can mean entirely or completely).
'h'+'all'='HALL'
'in' acts as a link.
(Other definitions for hall that I've seen before include "College dinner; passage" , "Large public building" , "Large meeting room" , "See 1" , "Large country house" .)