Great hotel rebuilt entirely (10)
I believe the answer is:
altogether
'entirely' is the definition.
('altogether' can be a synonym of 'entirely')
'great hotel rebuilt' is the wordplay.
'rebuilt' indicates anagramming the letters.
'great'+'hotel'='greathotel'
'greathotel' anagrammed gives 'ALTOGETHER'.
(Other definitions for altogether that I've seen before include "Completely, in total" , "totally" , "Wholly" , "Quite" , "special to get Hermes trousers" .)