Napoleon's associate saint? (6)

I believe the answer is:
helena
This could be a double definition.
'napoleon's' is the first definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'associate saint?' is the second definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
Can you help me to learn more?
(Other definitions for helena that I've seen before include "Hermia's friend, rival (MND)" , "dreamy girl" , "Girl's name - US state capital" , "Island saint in the South Atlantic" , "Could be Rubinstein" .)
