As a natural aptitude, it's most enlightening, we hear (5)
I believe the answer is:
flair
'as' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for flair that I've seen before include "Stylishness; talent" , "Taste" , "Bent" , "gift" , "Natural ability to do something well (5)" .)