Hibernian flag on hotel (5)
I believe the answer is:
irish
'hibernian' is the definition.
(I've seen this in another clue)
'flag on hotel' is the wordplay.
'flag' becomes 'iris' (synonyms).
'on' means one lot of letters go next to another.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'iris'+'h'='IRISH'
(Other definitions for irish that I've seen before include "From Dublin maybe" , "Hibernian -- breed of 4" , "race" , "Joyce was" , "A people, language and whiskey" .)