Foster sister? (5)
I believe the answer is:
nurse
I believe this clue is a double definition.
'foster' is the first definition.
(thesaurus)
'sister?' is the second definition.
(thesaurus)
(Other definitions for nurse that I've seen before include "Sister, e.g." , "Look after: entertain" , "Care for the sick" , "Carry on - - (film)" , "Hospital tender" .)