Both Uses

liaison
in
Anna Karenina
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Vronsky's mother, on hearing of his connection, was at first pleased at it, because nothing to her mind gave such a finishing touch to a brilliant young man as a liaison in the highest society; she was pleased, too, that Madame Karenina, who had so taken her fancy, and had talked so much of her son, was, after all, just like all other pretty and well-bred women,—at least according to the Countess Vronskaya's ideas.†
Part 2
She was vexed, too, that from all she could learn of this connection it was not that brilliant, graceful, worldly liaison which she would have welcomed, but a sort of Wertherish, desperate passion, so she was told, which might well lead him into imprudence.†
Part 2 *

Definitions:

(1) (liaison as in: She is their liaison)
a person with the role of increasing communication and cooperation between two organizations
(2) (meaning too rare to warrant focus)
In classic literature, liaison can refer to a sexual meeting or affair -- especially one kept secret. Liaison can also reference a communication link or an instance of communicating. Even more rarely, liaison can reference something used to thicken a sauce while cooking.