Newcomer sees rat miming badly (9)
I believe the answer is:
immigrant
'newcomer' is the definition.
(thesaurus)
'rat miming badly' is the wordplay.
'badly' indicates an anagram.
'rat'+'miming'='ratmiming'
'ratmiming' anagrammed gives 'IMMIGRANT'.
'sees' is the link.
(Other definitions for immigrant that I've seen before include "A settler from abroad" , "A new arrival" , "He's moved in" , "One moving from abroad" , "Settler, incomer" .)