Register in horrible resort (6)
I believe the answer is:
roster
'register' is the definition.
(I've seen this in another clue)
'horrible resort' is the wordplay.
'horrible' is an anagram indicator.
'resort' with letters rearranged gives 'ROSTER'.
'in' is the link.
(Other definitions for roster that I've seen before include "Resort (anag)" , "Roll" , "List of people's turn of duties" , "Schedule" , "List of duties and those who are to perform them" .)