From Longman Dictionary of Contemporary Englishassignationas‧sig‧na‧tion /ˌæsɪɡˈneɪʃən/ noun [countable] formal RELATIONSHIPa secret meeting, especially with someone you are having a romantic relationship with – often used humorously
Examples from the Corpus
assignation• Whatever he thought he was doing here, it doesn't look like an assignation, not with a woman anyway.• The mosaic spares none of the pertinent details of this ill-fated assignation.• The place was all tawdry bars, dance-halls and flop-houses that were also houses of assignation.• Allegations and denials about country hideaways, romantic recordings and Princess Di's secret assignations fly in all directions.• Would it now get about that Mrs Markham was a little peculiar or, worse still, that she had some assignation? 