conspiratorial

adj

1. Pertaining to conspiracy or conspirators.

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

   “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.””

2. (proscribed, sometimes)Believing in conspiracy theories.

   “Conspiratorial thinking is another predictor of vaccine hesitancy, according to the 2018 study.”