Protection, or Athena's shield (5)
I believe the answer is:
aegis
I believe this is a double definition.
'protection' is the first definition.
(aegis can mean someone's guidance or protection)
'athena's shield' is the second definition.
(I've seen this in another clue)
(Other definitions for aegis that I've seen before include "Protection (of someone)" , "Protection, backing" , "Protection or support" , "Kindly endorsement and guidance" , "Protection - patronage" .)