Terrible messes with rats in sewer (10)
I believe the answer is:
seamstress
'sewer' is the definition.
(thesaurus)
'terrible messes with rats' is the wordplay.
'terrible' indicates an anagram.
'with' says to put letters next to each other.
'messes' after 'rats' is 'ratsmesses'.
'ratsmesses' anagrammed gives 'SEAMSTRESS'.
'in' acts as a link.
(Other definitions for seamstress that I've seen before include "Midinette" , "Dressmaker" , "sewer" , "needlewoman" , "Woman who sews for a living" .)