Top escort (4)
I believe the answer is:
lead
This clue is a double definition.
'top' is the first definition.
(both can mean 'most important')
'escort' is the second definition.
(thesaurus)
(Other definitions for lead that I've seen before include "Chief part, element" , "Command; metal" , "Call the shots" , "guitar accessory?" , "Be in charge of, element" .)