To us, nurse is working hard (9)
I believe the answer is:
strenuous
'hard' is the definition.
(synonyms)
'to us nurse is working' is the wordplay.
'is working' is an anagram indicator.
'to'+'us'+'nurse'='tousnurse'
'tousnurse' with letters rearranged gives 'STRENUOUS'.
(Other definitions for strenuous that I've seen before include "Vigorous" , "with difficulty" , "Taxing" , "Requiring great effort" , "Needing much effort" .)