Servant left during rescue (5)
I believe the answer is:
slave
'servant' is the definition.
(thesaurus)
'left during rescue' is the wordplay.
'left' becomes 'l' (common abbreviation).
'during' is an insertion indicator.
'rescue' becomes 'save' (saving is a kind of rescuing).
'l' put within 'save' is 'SLAVE'.
(Other definitions for slave that I've seen before include "Person owned by another" , "Person who is the property of another" , "Work excessively hard" , "Person owned for work" , "Person in thraldom" .)