New field is classified (5)
I believe the answer is:
filed
'is classified' is the definition.
(thesaurus)
'new field' is the wordplay.
'new' indicates an anagram.
'field' anagrammed gives 'FILED'.
(Other definitions for filed that I've seen before include "Put away in a container for records" , "Worked with a tool" , "Placed in folder" , "Noted" , "arranged in a particular way" .)