Left a person unaccompanied (4)
I believe the answer is:
lone
'unaccompanied' is the definition.
(thesaurus)
'left a person' is the wordplay.
'left' becomes 'l' (common abbreviation).
'a person' becomes 'one' (**).
'l'+'one'='LONE'
(Other definitions for lone that I've seen before include "He likes to operate by himself" , "Unaccompanied" , "Companionless" , "The ... Ranger, fictional masked cowboy" , "Single and isolated" .)