Hospital doctor originally operating in Sumatra (10)
I believe the answer is:
sanatorium
'hospital' is the definition.
(sanatorium is a kind of hospital)
'doctor originally operating in sumatra' is the wordplay.
'doctor' indicates anagramming the letters.
'originally' indicates taking the first letters.
The initial letter of 'operating' is 'o'.
'o'+'in'+'sumatra'='oinsumatra'
'oinsumatra' anagrammed gives 'SANATORIUM'.
(Other definitions for sanatorium that I've seen before include "Health resort" , "convalescent home" , "health farm" , "Convalescent hospital" .)