corespondent

noun

1. One of two or more persons against whom a lawsuit is made; but especially a person charged with committing adultery with the defendant in a divorce proceeding.

   “It was simply a certified copy of the decree in the divorce case of a prominent society woman, Mrs. Percy Schermerman, who had named as corespondent a still more prominent woman, Mrs. Willoughby Worthington. The evidence had been sealed, and the yellower papers had toiled in vain to find out just who the prominent corespondent was.”