Assignation
Definition: time and place for a meeting
This seems to have a special designation for secret meetings, especially romantic meetings. An “assignation” is often implied to mean a sexual rendezvous.
Why I Looked It Up
In The English Assassin, regarding morally corrupt church elders, something was described as being:
[…] suitable for the cardinals private assignations
Postscript
Added on
In Alias Emma (another spy novel, coincidentally):
The plan was to text Chernov from her number, inviting him to an afternoon assignation at the Four Seasons.