Head of army, for example, is giving protection (5)
I believe the answer is:
Here is my best explanation:
'protection' is the definition.
(aegis is a kind of protection)
'head of army for example is' is the subsidiary indication.
'head of' says to take the initial letters.
'for example' becomes 'eg' ('e.g.' can be a synonym of 'for example').
The first letter of 'army' is 'a'.
'giving' is the link.
(Other definitions for aegis that I've seen before include "Protection or support", "Advocacy", "Protection or sponsorship", "Protection (originally of Zeus)", "Protection - guardianship", "Protection, backing", "Kindly endorsement and guidance", "Sponsorship", "Protection - patronage" and "Backing or support".)