Adjective

(en adjective)

stealthy

Exhibiting guilty or evasive secrecy.

* 1949 , George Orwell, Nineteen Eighty-Four , p31

But that was merely a piece of furtive knowledge which he happened to possess because his memory was not satisfactorily under control.

Adjective

(en adjective)

Pertaining to conspiracy or conspirators.

His conspiratorial whispers were soft, but that just attracted more attention.

* {{quote-book

, year=1960 , author= , title=(Jeeves in the Offing) , section=chapter X , passage=I pressed the button and he appeared, giving me, as he entered, the sort of conspiratorial' glance the acting secretary of a secret society would have given a friend on the membership roll. “Oh, Swordfish,” I said, having given him a '''conspiratorial''' glance in return, for one always likes to do the civil thing, “this is Mr Herring, who has come to join our little group.” He bowed from the waist, not that he had much waist. [...] “And when you have got him installed, perhaps I could have a word with you in your pantry,” I said, giving him a '''conspiratorial''' glance. “Certainly, sir,” he responded, giving me a '''conspiratorial''' glance. It was one of those big evenings for ' conspiratorial glances.}}