clandestine

adj

1. Done or kept in secret, sometimes to conceal an illicit or improper purpose.

   “clandestine military operations”

   “Monimia, who while she yielded to his earnest entreaties had always felt, from the natural rectitude of her understanding, the impropriety of their clandestine correspondence, would, he feared, be more than ever sensible of her indiscretion, when she found that a servant was entrusted with it...”

   “Whether the torments of absence were softened by a clandestine correspondence, let us not inquire. Mr. and Mrs. Morland never did.”

   “Wildeve's clandestine plan with her was to take a little gravel in his hand and hold it to the crevice at the top of the window shutter, which was on the outside, so that it should fall with a gentle rustle, resembling that of a mouse, between shutter and glass.”

   “Lady Bullingdon could not, of course, countenance such an arrangement for a moment, and the two unhappy persons escaped for a clandestine marriage.”

2. Not recognized as a regular member.