Detestable hotel, so am changing (9)
I believe the answer is:
loathsome
'detestable' is the definition.
(I've seen this before)
'hotel so am changing' is the wordplay.
'changing' indicates an anagram.
'hotel'+'so'+'am'='hotelsoam'
'hotelsoam' is an anagram of 'LOATHSOME'.
(Other definitions for loathsome that I've seen before include "gross" , "Detestable" , "Repulsive" , "Hateful" , "Horrid" .)