Fake rep upset nurse (7)
I believe the answer is:
pretend
'fake' is the definition.
(thesaurus)
'rep upset nurse' is the wordplay.
'upset' is an anagram indicator.
'nurse' becomes 'tend' (I've seen this before).
'rep' with letters rearranged gives 'pre'.
'pre'+'tend'='PRETEND'
(Other definitions for pretend that I've seen before include "Simulated" , "Behave unnaturally" , "keep up appearances" , "Suppose" , "Simulate - make up" .)