This is the 11693rd most frequent French word.
secrète
Hidden or private.
Here, 'secrète' describes the nature of her life as being hidden or mysterious.
Elle mène une vie secrète, pleine de mystère.
She leads a secret life, full of mystery.
In this instance, 'secrète' is used to characterize the key as being undisclosed or only known by certain individuals.
Il détient une clé secrète qui ouvre une porte mystérieuse.
He possesses a secret key that opens a mysterious door.
Here, 'secrète' indicates that the meeting was not publicly known or open to the general public.