Smart hotel guarded by top soldier initially (4)
I believe the answer is:
chic
'smart' is the definition.
(synonyms)
'hotel guarded by top soldier initially' is the wordplay.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'guarded by' means one lot of letters goes inside another.
'top soldier initially' becomes 'CIC' (initials for Commander in Chief).
'h' put into 'cic' is 'CHIC'.
(Other definitions for chic that I've seen before include "Unwanted sounds" , "style?" , "Stylish and elegant - in France" , "Fashionably elegant" , "Well turned out" .)